:: GRAPH_3 semantic presentation

begin

definition
let D be set ;
let T be non empty FinSequenceSet of D;
let S be non empty Subset of T;
:: original: Element
redefine mode Element of S ->  FinSequence of D;
coherence
 for b1 being Element of S holds b1 is FinSequence of D
proof
let x be Element of S; ::_thesis: x is FinSequence of D
 x is Element of T ;
hence  x is FinSequence of D ; ::_thesis: verum
end;
end;

registration
let i, j be even Integer;
clusteri - j ->  even ;
coherence
 i - j is even
proof
 2 divides j by ABIAN:def_1;
then consider l being Integer such that
A1: j = 2 * l by INT_1:def_3;
 2 divides i by ABIAN:def_1;
then consider k being Integer such that
A2: i = 2 * k by INT_1:def_3;
 i - j = 2 * (k - l) by A2, A1;
hence  i - j is even ; ::_thesis: verum
end;
end;

theorem :: GRAPH_3:1
for i, j being Integer holds
( ( i is even iff j is even ) iff i - j is even ) ;

Lm1:  for p being FinSequence
for m, n being Element of NAT st 1 <= m & m <= n + 1 & n <= len p holds
( (len ((m,n) -cut p)) + m = n + 1 & ( for i being Element of NAT st i < len ((m,n) -cut p) holds
((m,n) -cut p) . (i + 1) = p . (m + i) ) )
proof
let p be FinSequence; ::_thesis: for m, n being Element of NAT st 1 <= m & m <= n + 1 & n <= len p holds
( (len ((m,n) -cut p)) + m = n + 1 & ( for i being Element of NAT st i < len ((m,n) -cut p) holds
((m,n) -cut p) . (i + 1) = p . (m + i) ) )
let m, n be Element of NAT ; ::_thesis: ( 1 <= m & m <= n + 1 & n <= len p implies ( (len ((m,n) -cut p)) + m = n + 1 & ( for i being Element of NAT st i < len ((m,n) -cut p) holds
((m,n) -cut p) . (i + 1) = p . (m + i) ) ) )
assume that
A1: 1 <= m and
A2: m <= n + 1 and
A3: n <= len p ; ::_thesis: ( (len ((m,n) -cut p)) + m = n + 1 & ( for i being Element of NAT st i < len ((m,n) -cut p) holds
((m,n) -cut p) . (i + 1) = p . (m + i) ) )
A4: ( m = n + 1 or m < n + 1 ) by A2, XXREAL_0:1;
percases ( m = n + 1 or m <= n ) by A4, NAT_1:13;
supposeA5: m = n + 1 ; ::_thesis: ( (len ((m,n) -cut p)) + m = n + 1 & ( for i being Element of NAT st i < len ((m,n) -cut p) holds
((m,n) -cut p) . (i + 1) = p . (m + i) ) )
then  n < m by XREAL_1:29;
then  (m,n) -cut p = {} by GRAPH_2:def_1;
hence  (len ((m,n) -cut p)) + m = n + 1 by A5, CARD_1:27; ::_thesis: for i being Element of NAT st i < len ((m,n) -cut p) holds
((m,n) -cut p) . (i + 1) = p . (m + i)
 ( not 1 <= m or not m <= n or not n <= len p ) by A5, XREAL_1:29;
hence  for i being Element of NAT st i < len ((m,n) -cut p) holds
((m,n) -cut p) . (i + 1) = p . (m + i) by CARD_1:27, GRAPH_2:def_1; ::_thesis: verum
end;
suppose m <= n ; ::_thesis: ( (len ((m,n) -cut p)) + m = n + 1 & ( for i being Element of NAT st i < len ((m,n) -cut p) holds
((m,n) -cut p) . (i + 1) = p . (m + i) ) )
hence  ( (len ((m,n) -cut p)) + m = n + 1 & ( for i being Element of NAT st i < len ((m,n) -cut p) holds
((m,n) -cut p) . (i + 1) = p . (m + i) ) ) by A1, A3, GRAPH_2:def_1; ::_thesis: verum
end;
end;
end;

theorem Th2: :: GRAPH_3:2
for p being FinSequence
for m, n, a being Element of NAT st a in dom ((m,n) -cut p) holds
ex k being Element of NAT st
( k in dom p & p . k = ((m,n) -cut p) . a & k + 1 = m + a & m <= k & k <= n )
proof
let p be FinSequence; ::_thesis: for m, n, a being Element of NAT st a in dom ((m,n) -cut p) holds
ex k being Element of NAT st
( k in dom p & p . k = ((m,n) -cut p) . a & k + 1 = m + a & m <= k & k <= n )
let m, n, a be Element of NAT ; ::_thesis: ( a in dom ((m,n) -cut p) implies ex k being Element of NAT st
( k in dom p & p . k = ((m,n) -cut p) . a & k + 1 = m + a & m <= k & k <= n ) )
assume A1: a in dom ((m,n) -cut p) ; ::_thesis: ex k being Element of NAT st
( k in dom p & p . k = ((m,n) -cut p) . a & k + 1 = m + a & m <= k & k <= n )
set cp = (m,n) -cut p;
A2: a <= len ((m,n) -cut p) by A1, FINSEQ_3:25;
percases ( ( 1 <= m & m <= n & n <= len p ) or not 1 <= m or not m <= n or not n <= len p ) ;
supposeA3: ( 1 <= m & m <= n & n <= len p ) ; ::_thesis: ex k being Element of NAT st
( k in dom p & p . k = ((m,n) -cut p) . a & k + 1 = m + a & m <= k & k <= n )
 0 + 1 <= a by A1, FINSEQ_3:25;
then consider i1 being Element of NAT  such that
 0 <= i1 and
A4: i1 < len ((m,n) -cut p) and
A5: a = i1 + 1 by A2, GRAPH_2:1;
take k = m + i1; ::_thesis: ( k in dom p & p . k = ((m,n) -cut p) . a & k + 1 = m + a & m <= k & k <= n )
 m <= k by NAT_1:11;
then A6: 1 <= k by A3, XXREAL_0:2;
A7: (len ((m,n) -cut p)) + m = n + 1 by A3, GRAPH_2:def_1;
A8: m + i1 < m + (len ((m,n) -cut p)) by A4, XREAL_1:6;
then  m + i1 <= n by A7, NAT_1:13;
then  k <= len p by A3, XXREAL_0:2;
hence  k in dom p by A6, FINSEQ_3:25; ::_thesis: ( p . k = ((m,n) -cut p) . a & k + 1 = m + a & m <= k & k <= n )
thus  p . k = ((m,n) -cut p) . a by A3, A4, A5, GRAPH_2:def_1; ::_thesis: ( k + 1 = m + a & m <= k & k <= n )
thus  k + 1 = m + a by A5; ::_thesis: ( m <= k & k <= n )
thus  ( m <= k & k <= n ) by A7, A8, NAT_1:11, NAT_1:13; ::_thesis: verum
end;
suppose ( not 1 <= m or not m <= n or not n <= len p ) ; ::_thesis: ex k being Element of NAT st
( k in dom p & p . k = ((m,n) -cut p) . a & k + 1 = m + a & m <= k & k <= n )
hence  ex k being Element of NAT st
( k in dom p & p . k = ((m,n) -cut p) . a & k + 1 = m + a & m <= k & k <= n ) by A1, GRAPH_2:def_1, RELAT_1:38; ::_thesis: verum
end;
end;
end;

definition
let G be Graph;
mode Vertex of G is Element of the carrier of G;
end;


theorem Th3: :: GRAPH_3:3
for G being Graph
for c being Chain of G
for vs being FinSequence of the carrier of G st vs is_vertex_seq_of c holds
not vs is empty
proof
let G be Graph; ::_thesis: for c being Chain of G
for vs being FinSequence of the carrier of G st vs is_vertex_seq_of c holds
not vs is empty
let c be Chain of G; ::_thesis: for vs being FinSequence of the carrier of G st vs is_vertex_seq_of c holds
not vs is empty
let vs be FinSequence of the carrier of G; ::_thesis: ( vs is_vertex_seq_of c implies not vs is empty )
assume  vs is_vertex_seq_of c ; ::_thesis: not vs is empty
then  len vs = (len c) + 1 by GRAPH_2:def_6;
hence  not vs is empty ; ::_thesis: verum
end;

Lm2:  for G being Graph
for p being Path of G
for n, m being Element of NAT st 1 <= n & n <= len p & 1 <= m & m <= len p & n <> m holds
p . n <> p . m
proof
let G be Graph; ::_thesis: for p being Path of G
for n, m being Element of NAT st 1 <= n & n <= len p & 1 <= m & m <= len p & n <> m holds
p . n <> p . m
let p be Path of G; ::_thesis: for n, m being Element of NAT st 1 <= n & n <= len p & 1 <= m & m <= len p & n <> m holds
p . n <> p . m
let n, m be Element of NAT ; ::_thesis: ( 1 <= n & n <= len p & 1 <= m & m <= len p & n <> m implies p . n <> p . m )
assume that
A1: ( 1 <= n & n <= len p & 1 <= m & m <= len p ) and
A2: n <> m ; ::_thesis: p . n <> p . m
 ( n in dom p & m in dom p ) by A1, FINSEQ_3:25;
hence  p . n <> p . m by A2, FUNCT_1:def_4; ::_thesis: verum
end;

theorem Th4: :: GRAPH_3:4
for G being Graph
for e being set st e in the carrier' of G holds
<*e*> is Path of G
proof
let G be Graph; ::_thesis: for e being set st e in the carrier' of G holds
<*e*> is Path of G
let e be set ; ::_thesis: ( e in the carrier' of G implies <*e*> is Path of G )
assume  e in the carrier' of G ; ::_thesis: <*e*> is Path of G
then reconsider c = <*e*> as Chain of G by MSSCYC_1:5;
now__::_thesis:_for_n,_m_being_Element_of_NAT_st_1_<=_n_&_n_<_m_&_m_<=_len_c_holds_
c_._n_<>_c_._m
let n, m be Element of NAT ; ::_thesis: ( 1 <= n & n < m & m <= len c implies c . n <> c . m )
A1: len c = 1 by FINSEQ_1:39;
assume  ( 1 <= n & n < m & m <= len c ) ; ::_thesis: c . n <> c . m
hence  c . n <> c . m by A1, XXREAL_0:2; ::_thesis: verum
end;
hence  <*e*> is Path of G by GRAPH_1:def_16; ::_thesis: verum
end;

theorem Th5: :: GRAPH_3:5
for G being Graph
for p being Path of G
for m, n being Element of NAT holds (m,n) -cut p is Path of G
proof
let G be Graph; ::_thesis: for p being Path of G
for m, n being Element of NAT holds (m,n) -cut p is Path of G
let p be Path of G; ::_thesis: for m, n being Element of NAT holds (m,n) -cut p is Path of G
let m, n be Element of NAT ; ::_thesis: (m,n) -cut p is Path of G
percases ( not 1 <= m or not n <= len p or m > n or ( 1 <= m & m <= n & n <= len p ) ) ;
suppose ( not 1 <= m or not n <= len p or m > n ) ; ::_thesis: (m,n) -cut p is Path of G
then  (m,n) -cut p = {} by GRAPH_2:def_1;
hence  (m,n) -cut p is Path of G by GRAPH_1:14; ::_thesis: verum
end;
suppose ( 1 <= m & m <= n & n <= len p ) ; ::_thesis: (m,n) -cut p is Path of G
then reconsider q = (m,n) -cut p as Chain of G by GRAPH_2:41;
assume  (m,n) -cut p is not Path of G ; ::_thesis: contradiction
then consider a, b being Element of NAT  such that
A1: 1 <= a and
A2: a < b and
A3: b <= len q and
A4: q . a = q . b by GRAPH_1:def_16;
 1 <= b by A1, A2, XXREAL_0:2;
then  b in dom q by A3, FINSEQ_3:25;
then consider kb being Element of NAT  such that
A5: ( kb in dom p & p . kb = q . b ) and
A6: kb + 1 = m + b and
 m <= kb and
 kb <= n by Th2;
 a <= len q by A2, A3, XXREAL_0:2;
then  a in dom q by A1, FINSEQ_3:25;
then consider ka being Element of NAT  such that
A7: ( ka in dom p & p . ka = q . a ) and
A8: ka + 1 = m + a and
 m <= ka and
 ka <= n by Th2;
 ka = kb by A4, A7, A5, FUNCT_1:def_4;
hence  contradiction by A2, A8, A6; ::_thesis: verum
end;
end;
end;

theorem Th6: :: GRAPH_3:6
for G being Graph
for p1, p2 being Path of G
for vs1, vs2 being FinSequence of the carrier of G st rng p1 misses rng p2 & vs1 is_vertex_seq_of p1 & vs2 is_vertex_seq_of p2 & vs1 . (len vs1) = vs2 . 1 holds
p1 ^ p2 is Path of G
proof
let G be Graph; ::_thesis: for p1, p2 being Path of G
for vs1, vs2 being FinSequence of the carrier of G st rng p1 misses rng p2 & vs1 is_vertex_seq_of p1 & vs2 is_vertex_seq_of p2 & vs1 . (len vs1) = vs2 . 1 holds
p1 ^ p2 is Path of G
let p1, p2 be Path of G; ::_thesis: for vs1, vs2 being FinSequence of the carrier of G st rng p1 misses rng p2 & vs1 is_vertex_seq_of p1 & vs2 is_vertex_seq_of p2 & vs1 . (len vs1) = vs2 . 1 holds
p1 ^ p2 is Path of G
let vs1, vs2 be FinSequence of the carrier of G; ::_thesis: ( rng p1 misses rng p2 & vs1 is_vertex_seq_of p1 & vs2 is_vertex_seq_of p2 & vs1 . (len vs1) = vs2 . 1 implies p1 ^ p2 is Path of G )
set c1 = p1;
set c2 = p2;
assume that
A1: rng p1 misses rng p2 and
A2: ( vs1 is_vertex_seq_of p1 & vs2 is_vertex_seq_of p2 & vs1 . (len vs1) = vs2 . 1 ) ; ::_thesis: p1 ^ p2 is Path of G
reconsider c = p1 ^ p2 as Chain of G by A2, GRAPH_2:43;
now__::_thesis:_for_n,_m_being_Element_of_NAT_st_1_<=_n_&_n_<_m_&_m_<=_len_c_holds_
not_c_._n_=_c_._m
let n, m be Element of NAT ; ::_thesis: ( 1 <= n & n < m & m <= len c implies not c . n = c . m )
assume that
A3: 1 <= n and
A4: n < m and
A5: m <= len c and
A6: c . n = c . m ; ::_thesis: contradiction
 1 <= m by A3, A4, XXREAL_0:2;
then A7: m in dom c by A5, FINSEQ_3:25;
 n <= len c by A4, A5, XXREAL_0:2;
then A8: n in dom c by A3, FINSEQ_3:25;
percases ( ( n in dom p1 & m in dom p1 ) or ( n in dom p1 & ex m2 being Nat st
( m2 in dom p2 & m = (len p1) + m2 ) ) or ( m in dom p1 & ex n2 being Nat st
( n2 in dom p2 & n = (len p1) + n2 ) ) or ( ex n2 being Nat st
( n2 in dom p2 & n = (len p1) + n2 ) & ex m2 being Nat st
( m2 in dom p2 & m = (len p1) + m2 ) ) ) by A8, A7, FINSEQ_1:25;
supposeA9: ( n in dom p1 & m in dom p1 ) ; ::_thesis: contradiction
then p1 . n = c . n by FINSEQ_1:def_7
.= p1 . m by A6, A9, FINSEQ_1:def_7 ;
hence  contradiction by A4, A9, FUNCT_1:def_4; ::_thesis: verum
end;
supposeA10: ( n in dom p1 & ex m2 being Nat st
( m2 in dom p2 & m = (len p1) + m2 ) ) ; ::_thesis: contradiction
then A11: p1 . n in rng p1 by FUNCT_1:def_3;
consider m2 being Nat such that
A12: m2 in dom p2 and
A13: m = (len p1) + m2 by A10;
A14: p2 . m2 in rng p2 by A12, FUNCT_1:def_3;
p1 . n = c . n by A10, FINSEQ_1:def_7
.= p2 . m2 by A6, A12, A13, FINSEQ_1:def_7 ;
hence  contradiction by A1, A11, A14, XBOOLE_0:3; ::_thesis: verum
end;
supposeA15: ( m in dom p1 & ex n2 being Nat st
( n2 in dom p2 & n = (len p1) + n2 ) ) ; ::_thesis: contradiction
then consider n2 being Nat such that
 n2 in dom p2 and
A16: n = (len p1) + n2 ;
 m <= len p1 by A15, FINSEQ_3:25;
then  (len p1) + n2 < len p1 by A4, A16, XXREAL_0:2;
hence  contradiction by NAT_1:11; ::_thesis: verum
end;
supposeA17: ( ex n2 being Nat st
( n2 in dom p2 & n = (len p1) + n2 ) & ex m2 being Nat st
( m2 in dom p2 & m = (len p1) + m2 ) ) ; ::_thesis: contradiction
then consider n2 being Nat such that
A18: ( n2 in dom p2 & n = (len p1) + n2 ) ;
consider m2 being Nat such that
A19: ( m2 in dom p2 & m = (len p1) + m2 ) by A17;
p2 . n2 = c . n by A18, FINSEQ_1:def_7
.= p2 . m2 by A6, A19, FINSEQ_1:def_7 ;
hence  contradiction by A4, A19, A18, FUNCT_1:def_4; ::_thesis: verum
end;
end;
end;
hence  p1 ^ p2 is Path of G by GRAPH_1:def_16; ::_thesis: verum
end;

theorem Th7: :: GRAPH_3:7
for G being Graph
for c being Chain of G st c = {} holds
c is cyclic
proof
let G be Graph; ::_thesis: for c being Chain of G st c = {} holds
c is cyclic
let c be Chain of G; ::_thesis: ( c = {} implies c is cyclic )
set v = the Vertex of G;
assume  c = {} ; ::_thesis: c is cyclic
then A1: <* the Vertex of G*> is_vertex_seq_of c by GRAPH_2:32;
 <* the Vertex of G*> . 1 = <* the Vertex of G*> . (len <* the Vertex of G*>) by FINSEQ_1:40;
hence  c is cyclic by A1, MSSCYC_1:def_2; ::_thesis: verum
end;

registration
let G be Graph;
cluster Relation-like NAT -defined the carrier' of G -valued Function-like one-to-one finite FinSequence-like FinSubsequence-like cyclic for Chain of G;
existence
 ex b1 being Path of G st b1 is cyclic
proof
reconsider p = {} as Path of G by GRAPH_1:14;
take  p ; ::_thesis: p is cyclic
thus  p is cyclic by Th7; ::_thesis: verum
end;
end;

theorem Th8: :: GRAPH_3:8
for G being Graph
for m being Element of NAT
for p being cyclic Path of G holds (((m + 1),(len p)) -cut p) ^ ((1,m) -cut p) is cyclic Path of G
proof
let G be Graph; ::_thesis: for m being Element of NAT
for p being cyclic Path of G holds (((m + 1),(len p)) -cut p) ^ ((1,m) -cut p) is cyclic Path of G
let m be Element of NAT ; ::_thesis: for p being cyclic Path of G holds (((m + 1),(len p)) -cut p) ^ ((1,m) -cut p) is cyclic Path of G
let p be cyclic Path of G; ::_thesis: (((m + 1),(len p)) -cut p) ^ ((1,m) -cut p) is cyclic Path of G
percases ( m = 0 or ( 1 <= m & len p = m ) or ( 1 <= m & len p < m ) or ( 1 <= m & m < len p ) ) by NAT_1:14, XXREAL_0:1;
supposeA1: m = 0 ; ::_thesis: (((m + 1),(len p)) -cut p) ^ ((1,m) -cut p) is cyclic Path of G
 0 <= len p ;
then  (len ((1,m) -cut p)) + 1 = 0 + 1 by A1, Lm1;
then A2: (1,m) -cut p = {} ;
 ((m + 1),(len p)) -cut p = p by A1, GRAPH_2:7;
hence  (((m + 1),(len p)) -cut p) ^ ((1,m) -cut p) is cyclic Path of G by A2, FINSEQ_1:34; ::_thesis: verum
end;
supposeA3: ( 1 <= m & len p = m ) ; ::_thesis: (((m + 1),(len p)) -cut p) ^ ((1,m) -cut p) is cyclic Path of G
 1 <= m + 1 by NAT_1:12;
then  (len (((m + 1),(len p)) -cut p)) + (m + 1) = (len p) + 1 by A3, Lm1;
then  ((m + 1),(len p)) -cut p = {} by A3;
then (((m + 1),(len p)) -cut p) ^ ((1,m) -cut p) = (1,m) -cut p by FINSEQ_1:34
.= p by A3, GRAPH_2:7 ;
hence  (((m + 1),(len p)) -cut p) ^ ((1,m) -cut p) is cyclic Path of G ; ::_thesis: verum
end;
supposeA4: ( 1 <= m & len p < m ) ; ::_thesis: (((m + 1),(len p)) -cut p) ^ ((1,m) -cut p) is cyclic Path of G
 m <= m + 1 by NAT_1:11;
then  len p < m + 1 by A4, XXREAL_0:2;
then A5: ((m + 1),(len p)) -cut p = {} by GRAPH_2:def_1;
 (1,m) -cut p = {} by A4, GRAPH_2:def_1;
then  (((m + 1),(len p)) -cut p) ^ ((1,m) -cut p) = {} by A5, FINSEQ_1:34;
hence  (((m + 1),(len p)) -cut p) ^ ((1,m) -cut p) is cyclic Path of G by Th7, GRAPH_1:14; ::_thesis: verum
end;
supposeA6: ( 1 <= m & m < len p ) ; ::_thesis: (((m + 1),(len p)) -cut p) ^ ((1,m) -cut p) is cyclic Path of G
set n1 = m;
set n = m + 1;
A7: 1 <= m + 1 by A6, NAT_1:13;
reconsider r1 = (1,m) -cut p, r2 = ((m + 1),(len p)) -cut p as Path of G by Th5;
consider vs being FinSequence of the carrier of G such that
A8: vs is_vertex_seq_of p by GRAPH_2:33;
reconsider vs1 = (1,(m + 1)) -cut vs, vs2 = ((m + 1),(len vs)) -cut vs as FinSequence of the carrier of G ;
A9: m + 1 <= len p by A6, NAT_1:13;
A10: len vs = (len p) + 1 by A8, GRAPH_2:def_6;
then A11: vs2 is_vertex_seq_of r2 by A7, A9, A8, GRAPH_2:42;
 len p <= (len p) + 1 by NAT_1:11;
then A12: m + 1 <= len vs by A9, A10, XXREAL_0:2;
then A13: m + 1 < (len vs) + 1 by NAT_1:13;
 (len vs1) + 1 = (m + 1) + 1 by A7, A12, GRAPH_2:def_1;
then A14: 1 < len vs1 by A6, NAT_1:13;
A15: vs1 is_vertex_seq_of r1 by A6, A8, GRAPH_2:42;
 len vs <= (len vs) + 1 by NAT_1:11;
then  m + 1 <= (len vs) + 1 by A12, XXREAL_0:2;
then  (len vs2) + (m + 1) = (len vs) + 1 by A7, Lm1;
then  1 + (m + 1) <= (len vs2) + (m + 1) by A13, NAT_1:13;
then A16: 1 <= len vs2 by XREAL_1:6;
reconsider vs9 = vs2 ^' vs1 as FinSequence of the carrier of G ;
set r = r2 ^ r1;
A17: vs . (len vs) = vs . 1 by A8, MSSCYC_1:6;
A18: ( vs1 . 1 = vs . 1 & vs2 . (len vs2) = vs . (len vs) ) by A7, A12, GRAPH_2:12;
then reconsider r = r2 ^ r1 as Chain of G by A17, A15, A11, GRAPH_2:43;
A19: vs9 is_vertex_seq_of r by A17, A15, A11, A18, GRAPH_2:44;
 p = r1 ^ r2 by A6, GRAPH_2:9;
then  rng r1 misses rng r2 by FINSEQ_3:91;
then reconsider r = r as Path of G by A17, A15, A11, A18, Th6;
 ( vs1 . (len vs1) = vs . (m + 1) & vs2 . 1 = vs . (m + 1) ) by A7, A12, GRAPH_2:12;
then vs9 . 1 = vs1 . (len vs1) by A16, GRAPH_2:14
.= vs9 . (len vs9) by A14, GRAPH_2:16 ;
then  r is cyclic Path of G by A19, MSSCYC_1:def_2;
hence  (((m + 1),(len p)) -cut p) ^ ((1,m) -cut p) is cyclic Path of G ; ::_thesis: verum
end;
end;
end;

theorem Th9: :: GRAPH_3:9
for G being Graph
for p being Path of G
for m being Element of NAT st m + 1 in dom p holds
( len ((((m + 1),(len p)) -cut p) ^ ((1,m) -cut p)) = len p & rng ((((m + 1),(len p)) -cut p) ^ ((1,m) -cut p)) = rng p & ((((m + 1),(len p)) -cut p) ^ ((1,m) -cut p)) . 1 = p . (m + 1) )
proof
let G be Graph; ::_thesis: for p being Path of G
for m being Element of NAT st m + 1 in dom p holds
( len ((((m + 1),(len p)) -cut p) ^ ((1,m) -cut p)) = len p & rng ((((m + 1),(len p)) -cut p) ^ ((1,m) -cut p)) = rng p & ((((m + 1),(len p)) -cut p) ^ ((1,m) -cut p)) . 1 = p . (m + 1) )
let p be Path of G; ::_thesis: for m being Element of NAT st m + 1 in dom p holds
( len ((((m + 1),(len p)) -cut p) ^ ((1,m) -cut p)) = len p & rng ((((m + 1),(len p)) -cut p) ^ ((1,m) -cut p)) = rng p & ((((m + 1),(len p)) -cut p) ^ ((1,m) -cut p)) . 1 = p . (m + 1) )
let m be Element of NAT ; ::_thesis: ( m + 1 in dom p implies ( len ((((m + 1),(len p)) -cut p) ^ ((1,m) -cut p)) = len p & rng ((((m + 1),(len p)) -cut p) ^ ((1,m) -cut p)) = rng p & ((((m + 1),(len p)) -cut p) ^ ((1,m) -cut p)) . 1 = p . (m + 1) ) )
set r2 = ((m + 1),(len p)) -cut p;
set r1 = (1,m) -cut p;
set r = (((m + 1),(len p)) -cut p) ^ ((1,m) -cut p);
set n = m + 1;
assume A1: m + 1 in dom p ; ::_thesis: ( len ((((m + 1),(len p)) -cut p) ^ ((1,m) -cut p)) = len p & rng ((((m + 1),(len p)) -cut p) ^ ((1,m) -cut p)) = rng p & ((((m + 1),(len p)) -cut p) ^ ((1,m) -cut p)) . 1 = p . (m + 1) )
then A2: m + 1 <= len p by FINSEQ_3:25;
then A3: m + 1 < (len p) + 1 by NAT_1:13;
 m <= m + 1 by NAT_1:11;
then A4: p = ((1,m) -cut p) ^ (((m + 1),(len p)) -cut p) by A2, GRAPH_2:9, XXREAL_0:2;
thus  len ((((m + 1),(len p)) -cut p) ^ ((1,m) -cut p)) = (len ((1,m) -cut p)) + (len (((m + 1),(len p)) -cut p)) by FINSEQ_1:22
.= len p by A4, FINSEQ_1:22 ; ::_thesis: ( rng ((((m + 1),(len p)) -cut p) ^ ((1,m) -cut p)) = rng p & ((((m + 1),(len p)) -cut p) ^ ((1,m) -cut p)) . 1 = p . (m + 1) )
thus  rng ((((m + 1),(len p)) -cut p) ^ ((1,m) -cut p)) = (rng ((1,m) -cut p)) \/ (rng (((m + 1),(len p)) -cut p)) by FINSEQ_1:31
.= rng p by A4, FINSEQ_1:31 ; ::_thesis: ((((m + 1),(len p)) -cut p) ^ ((1,m) -cut p)) . 1 = p . (m + 1)
A5: 1 <= m + 1 by A1, FINSEQ_3:25;
then  (len (((m + 1),(len p)) -cut p)) + (m + 1) = (len p) + 1 by A2, GRAPH_2:def_1;
then  1 + (m + 1) <= (len (((m + 1),(len p)) -cut p)) + (m + 1) by A3, NAT_1:13;
then A6: 1 <= len (((m + 1),(len p)) -cut p) by XREAL_1:6;
then  1 in dom (((m + 1),(len p)) -cut p) by FINSEQ_3:25;
hence ((((m + 1),(len p)) -cut p) ^ ((1,m) -cut p)) . 1 = (((m + 1),(len p)) -cut p) . (0 + 1) by FINSEQ_1:def_7
.= p . ((m + 1) + 0) by A5, A2, A6, GRAPH_2:def_1
.= p . (m + 1) ;
::_thesis: verum
end;

theorem Th10: :: GRAPH_3:10
for G being Graph
for n being Element of NAT
for p being cyclic Path of G st n in dom p holds
ex p9 being cyclic Path of G st
( p9 . 1 = p . n & len p9 = len p & rng p9 = rng p )
proof
let G be Graph; ::_thesis: for n being Element of NAT
for p being cyclic Path of G st n in dom p holds
ex p9 being cyclic Path of G st
( p9 . 1 = p . n & len p9 = len p & rng p9 = rng p )
let n be Element of NAT ; ::_thesis: for p being cyclic Path of G st n in dom p holds
ex p9 being cyclic Path of G st
( p9 . 1 = p . n & len p9 = len p & rng p9 = rng p )
let p be cyclic Path of G; ::_thesis: ( n in dom p implies ex p9 being cyclic Path of G st
( p9 . 1 = p . n & len p9 = len p & rng p9 = rng p ) )
assume A1: n in dom p ; ::_thesis: ex p9 being cyclic Path of G st
( p9 . 1 = p . n & len p9 = len p & rng p9 = rng p )
then A2: 1 <= n by FINSEQ_3:25;
percases ( n = 1 or 1 < n ) by A2, XXREAL_0:1;
supposeA3: n = 1 ; ::_thesis: ex p9 being cyclic Path of G st
( p9 . 1 = p . n & len p9 = len p & rng p9 = rng p )
take  p ; ::_thesis: ( p . 1 = p . n & len p = len p & rng p = rng p )
thus  ( p . 1 = p . n & len p = len p & rng p = rng p ) by A3; ::_thesis: verum
end;
suppose 1 < n ; ::_thesis: ex p9 being cyclic Path of G st
( p9 . 1 = p . n & len p9 = len p & rng p9 = rng p )
then  1 + 1 <= n by NAT_1:13;
then consider n1 being Element of NAT  such that
 1 <= n1 and
 n1 < n and
A4: n = n1 + 1 by GRAPH_2:1;
reconsider r = ((n,(len p)) -cut p) ^ ((1,n1) -cut p) as cyclic Path of G by A4, Th8;
take  r ; ::_thesis: ( r . 1 = p . n & len r = len p & rng r = rng p )
thus  ( r . 1 = p . n & len r = len p & rng r = rng p ) by A1, A4, Th9; ::_thesis: verum
end;
end;
end;

theorem Th11: :: GRAPH_3:11
for G being Graph
for e being set
for s, t being Vertex of G st s = the Source of G . e & t = the Target of G . e holds
<*t,s*> is_vertex_seq_of <*e*>
proof
let G be Graph; ::_thesis: for e being set
for s, t being Vertex of G st s = the Source of G . e & t = the Target of G . e holds
<*t,s*> is_vertex_seq_of <*e*>
let e be set ; ::_thesis: for s, t being Vertex of G st s = the Source of G . e & t = the Target of G . e holds
<*t,s*> is_vertex_seq_of <*e*>
let s, t be Element of the carrier of G; ::_thesis: ( s = the Source of G . e & t = the Target of G . e implies <*t,s*> is_vertex_seq_of <*e*> )
assume A1: ( s = the Source of G . e & t = the Target of G . e ) ; ::_thesis: <*t,s*> is_vertex_seq_of <*e*>
set c = <*e*>;
set vs = <*t,s*>;
A2: <*t,s*> /. (1 + 1) = s by FINSEQ_4:17;
A3: len <*e*> = 1 by FINSEQ_1:39;
hence  len <*t,s*> = (len <*e*>) + 1 by FINSEQ_1:44; :: according to GRAPH_2:def_6 ::_thesis: for b1 being Element of NAT holds
( not 1 <= b1 or not b1 <= len <*e*> or <*e*> . b1 joins <*t,s*> /. b1,<*t,s*> /. (b1 + 1) )
let n be Element of NAT ; ::_thesis: ( not 1 <= n or not n <= len <*e*> or <*e*> . n joins <*t,s*> /. n,<*t,s*> /. (n + 1) )
assume  ( 1 <= n & n <= len <*e*> ) ; ::_thesis: <*e*> . n joins <*t,s*> /. n,<*t,s*> /. (n + 1)
then A4: n = 1 by A3, XXREAL_0:1;
 ( <*e*> . 1 = e & <*t,s*> /. 1 = t ) by FINSEQ_1:40, FINSEQ_4:17;
hence  <*e*> . n joins <*t,s*> /. n,<*t,s*> /. (n + 1) by A1, A4, A2, GRAPH_1:def_12; ::_thesis: verum
end;

theorem Th12: :: GRAPH_3:12
for G being Graph
for c being Chain of G
for vs being FinSequence of the carrier of G
for e being set st e in the carrier' of G & vs is_vertex_seq_of c & vs . (len vs) = the Source of G . e holds
( c ^ <*e*> is Chain of G & ex vs9 being FinSequence of the carrier of G st
( vs9 = vs ^' <*( the Source of G . e),( the Target of G . e)*> & vs9 is_vertex_seq_of c ^ <*e*> & vs9 . 1 = vs . 1 & vs9 . (len vs9) = the Target of G . e ) )
proof
let G be Graph; ::_thesis: for c being Chain of G
for vs being FinSequence of the carrier of G
for e being set st e in the carrier' of G & vs is_vertex_seq_of c & vs . (len vs) = the Source of G . e holds
( c ^ <*e*> is Chain of G & ex vs9 being FinSequence of the carrier of G st
( vs9 = vs ^' <*( the Source of G . e),( the Target of G . e)*> & vs9 is_vertex_seq_of c ^ <*e*> & vs9 . 1 = vs . 1 & vs9 . (len vs9) = the Target of G . e ) )
let c be Chain of G; ::_thesis: for vs being FinSequence of the carrier of G
for e being set st e in the carrier' of G & vs is_vertex_seq_of c & vs . (len vs) = the Source of G . e holds
( c ^ <*e*> is Chain of G & ex vs9 being FinSequence of the carrier of G st
( vs9 = vs ^' <*( the Source of G . e),( the Target of G . e)*> & vs9 is_vertex_seq_of c ^ <*e*> & vs9 . 1 = vs . 1 & vs9 . (len vs9) = the Target of G . e ) )
let vs be FinSequence of the carrier of G; ::_thesis: for e being set st e in the carrier' of G & vs is_vertex_seq_of c & vs . (len vs) = the Source of G . e holds
( c ^ <*e*> is Chain of G & ex vs9 being FinSequence of the carrier of G st
( vs9 = vs ^' <*( the Source of G . e),( the Target of G . e)*> & vs9 is_vertex_seq_of c ^ <*e*> & vs9 . 1 = vs . 1 & vs9 . (len vs9) = the Target of G . e ) )
let e be set ; ::_thesis: ( e in the carrier' of G & vs is_vertex_seq_of c & vs . (len vs) = the Source of G . e implies ( c ^ <*e*> is Chain of G & ex vs9 being FinSequence of the carrier of G st
( vs9 = vs ^' <*( the Source of G . e),( the Target of G . e)*> & vs9 is_vertex_seq_of c ^ <*e*> & vs9 . 1 = vs . 1 & vs9 . (len vs9) = the Target of G . e ) ) )
assume that
A1: e in the carrier' of G and
A2: vs is_vertex_seq_of c ; ::_thesis: ( not vs . (len vs) = the Source of G . e or ( c ^ <*e*> is Chain of G & ex vs9 being FinSequence of the carrier of G st
( vs9 = vs ^' <*( the Source of G . e),( the Target of G . e)*> & vs9 is_vertex_seq_of c ^ <*e*> & vs9 . 1 = vs . 1 & vs9 . (len vs9) = the Target of G . e ) ) )
reconsider ec = <*e*> as Chain of G by A1, MSSCYC_1:5;
reconsider s = the Source of G . e, t = the Target of G . e as Vertex of G by A1, FUNCT_2:5;
reconsider vse = <*s,t*> as FinSequence of the carrier of G ;
A3: ( vse is_vertex_seq_of ec & vse . 1 = s ) by FINSEQ_1:44, MSSCYC_1:4;
assume A4: vs . (len vs) = the Source of G . e ; ::_thesis: ( c ^ <*e*> is Chain of G & ex vs9 being FinSequence of the carrier of G st
( vs9 = vs ^' <*( the Source of G . e),( the Target of G . e)*> & vs9 is_vertex_seq_of c ^ <*e*> & vs9 . 1 = vs . 1 & vs9 . (len vs9) = the Target of G . e ) )
hence  c ^ <*e*> is Chain of G by A2, A3, GRAPH_2:43; ::_thesis: ex vs9 being FinSequence of the carrier of G st
( vs9 = vs ^' <*( the Source of G . e),( the Target of G . e)*> & vs9 is_vertex_seq_of c ^ <*e*> & vs9 . 1 = vs . 1 & vs9 . (len vs9) = the Target of G . e )
reconsider ce = c ^ ec as Chain of G by A2, A4, A3, GRAPH_2:43;
take vs9 = vs ^' vse; ::_thesis: ( vs9 = vs ^' <*( the Source of G . e),( the Target of G . e)*> & vs9 is_vertex_seq_of c ^ <*e*> & vs9 . 1 = vs . 1 & vs9 . (len vs9) = the Target of G . e )
thus  vs9 = vs ^' <*( the Source of G . e),( the Target of G . e)*> ; ::_thesis: ( vs9 is_vertex_seq_of c ^ <*e*> & vs9 . 1 = vs . 1 & vs9 . (len vs9) = the Target of G . e )
 vs9 is_vertex_seq_of ce by A2, A4, A3, GRAPH_2:44;
hence  vs9 is_vertex_seq_of c ^ <*e*> ; ::_thesis: ( vs9 . 1 = vs . 1 & vs9 . (len vs9) = the Target of G . e )
 len vs = (len c) + 1 by A2, GRAPH_2:def_6;
then  1 <= len vs by NAT_1:11;
hence  vs9 . 1 = vs . 1 by GRAPH_2:14; ::_thesis: vs9 . (len vs9) = the Target of G . e
A5: len vse = 2 by FINSEQ_1:44;
then  vse . (len vse) = t by FINSEQ_1:44;
hence  vs9 . (len vs9) = the Target of G . e by A5, GRAPH_2:16; ::_thesis: verum
end;

theorem Th13: :: GRAPH_3:13
for G being Graph
for c being Chain of G
for vs being FinSequence of the carrier of G
for e being set st e in the carrier' of G & vs is_vertex_seq_of c & vs . (len vs) = the Target of G . e holds
( c ^ <*e*> is Chain of G & ex vs9 being FinSequence of the carrier of G st
( vs9 = vs ^' <*( the Target of G . e),( the Source of G . e)*> & vs9 is_vertex_seq_of c ^ <*e*> & vs9 . 1 = vs . 1 & vs9 . (len vs9) = the Source of G . e ) )
proof
let G be Graph; ::_thesis: for c being Chain of G
for vs being FinSequence of the carrier of G
for e being set st e in the carrier' of G & vs is_vertex_seq_of c & vs . (len vs) = the Target of G . e holds
( c ^ <*e*> is Chain of G & ex vs9 being FinSequence of the carrier of G st
( vs9 = vs ^' <*( the Target of G . e),( the Source of G . e)*> & vs9 is_vertex_seq_of c ^ <*e*> & vs9 . 1 = vs . 1 & vs9 . (len vs9) = the Source of G . e ) )
let c be Chain of G; ::_thesis: for vs being FinSequence of the carrier of G
for e being set st e in the carrier' of G & vs is_vertex_seq_of c & vs . (len vs) = the Target of G . e holds
( c ^ <*e*> is Chain of G & ex vs9 being FinSequence of the carrier of G st
( vs9 = vs ^' <*( the Target of G . e),( the Source of G . e)*> & vs9 is_vertex_seq_of c ^ <*e*> & vs9 . 1 = vs . 1 & vs9 . (len vs9) = the Source of G . e ) )
let vs be FinSequence of the carrier of G; ::_thesis: for e being set st e in the carrier' of G & vs is_vertex_seq_of c & vs . (len vs) = the Target of G . e holds
( c ^ <*e*> is Chain of G & ex vs9 being FinSequence of the carrier of G st
( vs9 = vs ^' <*( the Target of G . e),( the Source of G . e)*> & vs9 is_vertex_seq_of c ^ <*e*> & vs9 . 1 = vs . 1 & vs9 . (len vs9) = the Source of G . e ) )
let e be set ; ::_thesis: ( e in the carrier' of G & vs is_vertex_seq_of c & vs . (len vs) = the Target of G . e implies ( c ^ <*e*> is Chain of G & ex vs9 being FinSequence of the carrier of G st
( vs9 = vs ^' <*( the Target of G . e),( the Source of G . e)*> & vs9 is_vertex_seq_of c ^ <*e*> & vs9 . 1 = vs . 1 & vs9 . (len vs9) = the Source of G . e ) ) )
assume that
A1: e in the carrier' of G and
A2: vs is_vertex_seq_of c ; ::_thesis: ( not vs . (len vs) = the Target of G . e or ( c ^ <*e*> is Chain of G & ex vs9 being FinSequence of the carrier of G st
( vs9 = vs ^' <*( the Target of G . e),( the Source of G . e)*> & vs9 is_vertex_seq_of c ^ <*e*> & vs9 . 1 = vs . 1 & vs9 . (len vs9) = the Source of G . e ) ) )
reconsider ec = <*e*> as Chain of G by A1, MSSCYC_1:5;
reconsider s = the Source of G . e, t = the Target of G . e as Vertex of G by A1, FUNCT_2:5;
assume A3: vs . (len vs) = the Target of G . e ; ::_thesis: ( c ^ <*e*> is Chain of G & ex vs9 being FinSequence of the carrier of G st
( vs9 = vs ^' <*( the Target of G . e),( the Source of G . e)*> & vs9 is_vertex_seq_of c ^ <*e*> & vs9 . 1 = vs . 1 & vs9 . (len vs9) = the Source of G . e ) )
reconsider vse = <*t,s*> as FinSequence of the carrier of G ;
A4: ( vse is_vertex_seq_of ec & vse . 1 = t ) by Th11, FINSEQ_1:44;
hence  c ^ <*e*> is Chain of G by A2, A3, GRAPH_2:43; ::_thesis: ex vs9 being FinSequence of the carrier of G st
( vs9 = vs ^' <*( the Target of G . e),( the Source of G . e)*> & vs9 is_vertex_seq_of c ^ <*e*> & vs9 . 1 = vs . 1 & vs9 . (len vs9) = the Source of G . e )
reconsider ce = c ^ ec as Chain of G by A2, A3, A4, GRAPH_2:43;
take vs9 = vs ^' vse; ::_thesis: ( vs9 = vs ^' <*( the Target of G . e),( the Source of G . e)*> & vs9 is_vertex_seq_of c ^ <*e*> & vs9 . 1 = vs . 1 & vs9 . (len vs9) = the Source of G . e )
thus  vs9 = vs ^' <*( the Target of G . e),( the Source of G . e)*> ; ::_thesis: ( vs9 is_vertex_seq_of c ^ <*e*> & vs9 . 1 = vs . 1 & vs9 . (len vs9) = the Source of G . e )
 vs9 is_vertex_seq_of ce by A2, A3, A4, GRAPH_2:44;
hence  vs9 is_vertex_seq_of c ^ <*e*> ; ::_thesis: ( vs9 . 1 = vs . 1 & vs9 . (len vs9) = the Source of G . e )
 len vs = (len c) + 1 by A2, GRAPH_2:def_6;
then  1 <= len vs by NAT_1:11;
hence  vs9 . 1 = vs . 1 by GRAPH_2:14; ::_thesis: vs9 . (len vs9) = the Source of G . e
A5: len vse = 2 by FINSEQ_1:44;
then  vse . (len vse) = s by FINSEQ_1:44;
hence  vs9 . (len vs9) = the Source of G . e by A5, GRAPH_2:16; ::_thesis: verum
end;

Lm3:  for G being Graph
for c being Chain of G
for vs being FinSequence of the carrier of G st vs is_vertex_seq_of c holds
for n being Nat st 1 <= n & n <= len c holds
( 1 <= n & n <= len vs & 1 <= n + 1 & n + 1 <= len vs & ( ( vs . n = the Target of G . (c . n) & vs . (n + 1) = the Source of G . (c . n) ) or ( vs . n = the Source of G . (c . n) & vs . (n + 1) = the Target of G . (c . n) ) ) )
proof
let G be Graph; ::_thesis: for c being Chain of G
for vs being FinSequence of the carrier of G st vs is_vertex_seq_of c holds
for n being Nat st 1 <= n & n <= len c holds
( 1 <= n & n <= len vs & 1 <= n + 1 & n + 1 <= len vs & ( ( vs . n = the Target of G . (c . n) & vs . (n + 1) = the Source of G . (c . n) ) or ( vs . n = the Source of G . (c . n) & vs . (n + 1) = the Target of G . (c . n) ) ) )
let c be Chain of G; ::_thesis: for vs being FinSequence of the carrier of G st vs is_vertex_seq_of c holds
for n being Nat st 1 <= n & n <= len c holds
( 1 <= n & n <= len vs & 1 <= n + 1 & n + 1 <= len vs & ( ( vs . n = the Target of G . (c . n) & vs . (n + 1) = the Source of G . (c . n) ) or ( vs . n = the Source of G . (c . n) & vs . (n + 1) = the Target of G . (c . n) ) ) )
let vs be FinSequence of the carrier of G; ::_thesis: ( vs is_vertex_seq_of c implies for n being Nat st 1 <= n & n <= len c holds
( 1 <= n & n <= len vs & 1 <= n + 1 & n + 1 <= len vs & ( ( vs . n = the Target of G . (c . n) & vs . (n + 1) = the Source of G . (c . n) ) or ( vs . n = the Source of G . (c . n) & vs . (n + 1) = the Target of G . (c . n) ) ) ) )
assume A1: vs is_vertex_seq_of c ; ::_thesis: for n being Nat st 1 <= n & n <= len c holds
( 1 <= n & n <= len vs & 1 <= n + 1 & n + 1 <= len vs & ( ( vs . n = the Target of G . (c . n) & vs . (n + 1) = the Source of G . (c . n) ) or ( vs . n = the Source of G . (c . n) & vs . (n + 1) = the Target of G . (c . n) ) ) )
then A2: len vs = (len c) + 1 by GRAPH_2:def_6;
let n be Nat; ::_thesis: ( 1 <= n & n <= len c implies ( 1 <= n & n <= len vs & 1 <= n + 1 & n + 1 <= len vs & ( ( vs . n = the Target of G . (c . n) & vs . (n + 1) = the Source of G . (c . n) ) or ( vs . n = the Source of G . (c . n) & vs . (n + 1) = the Target of G . (c . n) ) ) ) )
assume that
A3: 1 <= n and
A4: n <= len c ; ::_thesis: ( 1 <= n & n <= len vs & 1 <= n + 1 & n + 1 <= len vs & ( ( vs . n = the Target of G . (c . n) & vs . (n + 1) = the Source of G . (c . n) ) or ( vs . n = the Source of G . (c . n) & vs . (n + 1) = the Target of G . (c . n) ) ) )
thus  1 <= n by A3; ::_thesis: ( n <= len vs & 1 <= n + 1 & n + 1 <= len vs & ( ( vs . n = the Target of G . (c . n) & vs . (n + 1) = the Source of G . (c . n) ) or ( vs . n = the Source of G . (c . n) & vs . (n + 1) = the Target of G . (c . n) ) ) )
 len c <= (len c) + 1 by NAT_1:11;
hence A5: n <= len vs by A4, A2, XXREAL_0:2; ::_thesis: ( 1 <= n + 1 & n + 1 <= len vs & ( ( vs . n = the Target of G . (c . n) & vs . (n + 1) = the Source of G . (c . n) ) or ( vs . n = the Source of G . (c . n) & vs . (n + 1) = the Target of G . (c . n) ) ) )
thus  1 <= n + 1 by NAT_1:11; ::_thesis: ( n + 1 <= len vs & ( ( vs . n = the Target of G . (c . n) & vs . (n + 1) = the Source of G . (c . n) ) or ( vs . n = the Source of G . (c . n) & vs . (n + 1) = the Target of G . (c . n) ) ) )
thus A6: n + 1 <= len vs by A4, A2, XREAL_1:6; ::_thesis: ( ( vs . n = the Target of G . (c . n) & vs . (n + 1) = the Source of G . (c . n) ) or ( vs . n = the Source of G . (c . n) & vs . (n + 1) = the Target of G . (c . n) ) )
reconsider n = n as Element of NAT by ORDINAL1:def_12;
A7: vs . n = vs /. n by A3, A5, FINSEQ_4:15;
A8: vs . (n + 1) = vs /. (n + 1) by A6, FINSEQ_4:15, NAT_1:11;
 c . n joins vs /. n,vs /. (n + 1) by A1, A3, A4, GRAPH_2:def_6;
hence  ( ( vs . n = the Target of G . (c . n) & vs . (n + 1) = the Source of G . (c . n) ) or ( vs . n = the Source of G . (c . n) & vs . (n + 1) = the Target of G . (c . n) ) ) by A7, A8, GRAPH_1:def_12; ::_thesis: verum
end;

theorem :: GRAPH_3:14
for G being Graph
for c being Chain of G
for vs being FinSequence of the carrier of G st vs is_vertex_seq_of c holds
for n being Element of NAT holds
( not n in dom c or ( vs . n = the Target of G . (c . n) & vs . (n + 1) = the Source of G . (c . n) ) or ( vs . n = the Source of G . (c . n) & vs . (n + 1) = the Target of G . (c . n) ) )
proof
let G be Graph; ::_thesis: for c being Chain of G
for vs being FinSequence of the carrier of G st vs is_vertex_seq_of c holds
for n being Element of NAT holds
( not n in dom c or ( vs . n = the Target of G . (c . n) & vs . (n + 1) = the Source of G . (c . n) ) or ( vs . n = the Source of G . (c . n) & vs . (n + 1) = the Target of G . (c . n) ) )
let c be Chain of G; ::_thesis: for vs being FinSequence of the carrier of G st vs is_vertex_seq_of c holds
for n being Element of NAT holds
( not n in dom c or ( vs . n = the Target of G . (c . n) & vs . (n + 1) = the Source of G . (c . n) ) or ( vs . n = the Source of G . (c . n) & vs . (n + 1) = the Target of G . (c . n) ) )
let vs be FinSequence of the carrier of G; ::_thesis: ( vs is_vertex_seq_of c implies for n being Element of NAT holds
( not n in dom c or ( vs . n = the Target of G . (c . n) & vs . (n + 1) = the Source of G . (c . n) ) or ( vs . n = the Source of G . (c . n) & vs . (n + 1) = the Target of G . (c . n) ) ) )
assume A1: vs is_vertex_seq_of c ; ::_thesis: for n being Element of NAT holds
( not n in dom c or ( vs . n = the Target of G . (c . n) & vs . (n + 1) = the Source of G . (c . n) ) or ( vs . n = the Source of G . (c . n) & vs . (n + 1) = the Target of G . (c . n) ) )
let n be Element of NAT ; ::_thesis: ( not n in dom c or ( vs . n = the Target of G . (c . n) & vs . (n + 1) = the Source of G . (c . n) ) or ( vs . n = the Source of G . (c . n) & vs . (n + 1) = the Target of G . (c . n) ) )
assume  n in dom c ; ::_thesis: ( ( vs . n = the Target of G . (c . n) & vs . (n + 1) = the Source of G . (c . n) ) or ( vs . n = the Source of G . (c . n) & vs . (n + 1) = the Target of G . (c . n) ) )
then  ( 1 <= n & n <= len c ) by FINSEQ_3:25;
hence  ( ( vs . n = the Target of G . (c . n) & vs . (n + 1) = the Source of G . (c . n) ) or ( vs . n = the Source of G . (c . n) & vs . (n + 1) = the Target of G . (c . n) ) ) by A1, Lm3; ::_thesis: verum
end;

theorem Th15: :: GRAPH_3:15
for G being Graph
for c being Chain of G
for vs being FinSequence of the carrier of G
for e being set st vs is_vertex_seq_of c & e in rng c holds
( the Target of G . e in rng vs & the Source of G . e in rng vs )
proof
let G be Graph; ::_thesis: for c being Chain of G
for vs being FinSequence of the carrier of G
for e being set st vs is_vertex_seq_of c & e in rng c holds
( the Target of G . e in rng vs & the Source of G . e in rng vs )
let c be Chain of G; ::_thesis: for vs being FinSequence of the carrier of G
for e being set st vs is_vertex_seq_of c & e in rng c holds
( the Target of G . e in rng vs & the Source of G . e in rng vs )
let vs be FinSequence of the carrier of G; ::_thesis: for e being set st vs is_vertex_seq_of c & e in rng c holds
( the Target of G . e in rng vs & the Source of G . e in rng vs )
let e be set ; ::_thesis: ( vs is_vertex_seq_of c & e in rng c implies ( the Target of G . e in rng vs & the Source of G . e in rng vs ) )
assume that
A1: vs is_vertex_seq_of c and
A2: e in rng c ; ::_thesis: ( the Target of G . e in rng vs & the Source of G . e in rng vs )
 c is FinSequence of the carrier' of G by MSSCYC_1:def_1;
then A3: rng c c= the carrier' of G by FINSEQ_1:def_4;
then reconsider e9 = e as Element of the carrier' of G by A2;
reconsider t = the Target of G . e, s = the Source of G . e as Vertex of G by A2, A3, FUNCT_2:5;
 e9 in rng c by A2;
then  ( t in G -VSet (rng c) & s in G -VSet (rng c) ) ;
hence  ( the Target of G . e in rng vs & the Source of G . e in rng vs ) by A1, A2, GRAPH_2:31, RELAT_1:38; ::_thesis: verum
end;

definition
let G be Graph;
let X be set ;
:: original: -VSet
redefine funcG -VSet X ->  Subset of the carrier of G;
coherence
 G -VSet X is Subset of the carrier of G
proof
defpred S1[ set ] means  ex e being Element of the carrier' of G st
( e in X & ( $1 = the Source of G . e or $1 = the Target of G . e ) );
  {  v where v is Vertex of G : S1[v]  }  is Subset of the carrier of G from DOMAIN_1:sch_7();
hence  G -VSet X is Subset of the carrier of G ; ::_thesis: verum
end;
end;

theorem Th16: :: GRAPH_3:16
for G being Graph holds G -VSet {} = {}
proof
let G be Graph; ::_thesis: G -VSet {} = {}
assume  not G -VSet {} = {} ; ::_thesis: contradiction
then consider x being set  such that
A1: x in G -VSet {} by XBOOLE_0:def_1;
 ex v being Vertex of G st
( x = v & ex e being Element of the carrier' of G st
( e in {} & ( v = the Source of G . e or v = the Target of G . e ) ) ) by A1;
hence  contradiction ; ::_thesis: verum
end;

theorem Th17: :: GRAPH_3:17
for G being Graph
for e, X being set st e in the carrier' of G & e in X holds
not G -VSet X is empty
proof
let G be Graph; ::_thesis: for e, X being set st e in the carrier' of G & e in X holds
not G -VSet X is empty
let e, X be set ; ::_thesis: ( e in the carrier' of G & e in X implies not G -VSet X is empty )
assume that
A1: e in the carrier' of G and
A2: e in X ; ::_thesis: not G -VSet X is empty
reconsider v = the Source of G . e as Vertex of G by A1, FUNCT_2:5;
 v in G -VSet X by A1, A2;
hence  not G -VSet X is empty ; ::_thesis: verum
end;

theorem Th18: :: GRAPH_3:18
for G being Graph holds
( G is connected iff for v1, v2 being Vertex of G st v1 <> v2 holds
ex c being Chain of G ex vs being FinSequence of the carrier of G st
( not c is empty & vs is_vertex_seq_of c & vs . 1 = v1 & vs . (len vs) = v2 ) )
proof
let G be Graph; ::_thesis: ( G is connected iff for v1, v2 being Vertex of G st v1 <> v2 holds
ex c being Chain of G ex vs being FinSequence of the carrier of G st
( not c is empty & vs is_vertex_seq_of c & vs . 1 = v1 & vs . (len vs) = v2 ) )
set E = the carrier' of G;
set S = the Source of G;
set T = the Target of G;
thus  ( G is connected implies for v1, v2 being Vertex of G st v1 <> v2 holds
ex c being Chain of G ex vs being FinSequence of the carrier of G st
( not c is empty & vs is_vertex_seq_of c & vs . 1 = v1 & vs . (len vs) = v2 ) ) ::_thesis: ( ( for v1, v2 being Vertex of G st v1 <> v2 holds
ex c being Chain of G ex vs being FinSequence of the carrier of G st
( not c is empty & vs is_vertex_seq_of c & vs . 1 = v1 & vs . (len vs) = v2 ) ) implies G is connected )
proof
reconsider V = the carrier of G as non empty set ;
assume A1: G is connected ; ::_thesis: for v1, v2 being Vertex of G st v1 <> v2 holds
ex c being Chain of G ex vs being FinSequence of the carrier of G st
( not c is empty & vs is_vertex_seq_of c & vs . 1 = v1 & vs . (len vs) = v2 )
let v1, v2 be Vertex of G; ::_thesis: ( v1 <> v2 implies ex c being Chain of G ex vs being FinSequence of the carrier of G st
( not c is empty & vs is_vertex_seq_of c & vs . 1 = v1 & vs . (len vs) = v2 ) )
set V1 =  {  v where v is Element of V : ( v = v1 or ex c being Chain of G ex vs being FinSequence of the carrier of G st
( not c is empty & vs is_vertex_seq_of c & vs . 1 = v1 & vs . (len vs) = v ) )  }  ;
set V2 = V \  {  v where v is Element of V : ( v = v1 or ex c being Chain of G ex vs being FinSequence of the carrier of G st
( not c is empty & vs is_vertex_seq_of c & vs . 1 = v1 & vs . (len vs) = v ) )  }  ;
 v1 in  {  v where v is Element of V : ( v = v1 or ex c being Chain of G ex vs being FinSequence of the carrier of G st
( not c is empty & vs is_vertex_seq_of c & vs . 1 = v1 & vs . (len vs) = v ) )  }  ;
then reconsider V1 =  {  v where v is Element of V : ( v = v1 or ex c being Chain of G ex vs being FinSequence of the carrier of G st
( not c is empty & vs is_vertex_seq_of c & vs . 1 = v1 & vs . (len vs) = v ) )  }  as non empty set ;
assume A2: v1 <> v2 ; ::_thesis: ex c being Chain of G ex vs being FinSequence of the carrier of G st
( not c is empty & vs is_vertex_seq_of c & vs . 1 = v1 & vs . (len vs) = v2 )
assume A3: for c being Chain of G
for vs being FinSequence of the carrier of G holds
( c is empty or not vs is_vertex_seq_of c or not vs . 1 = v1 or not vs . (len vs) = v2 ) ; ::_thesis: contradiction
now__::_thesis:_not_v2_in_V1
assume  v2 in V1 ; ::_thesis: contradiction
then  ex v being Vertex of G st
( v = v2 & ( v = v1 or ex c being Chain of G ex vs being FinSequence of the carrier of G st
( not c is empty & vs is_vertex_seq_of c & vs . 1 = v1 & vs . (len vs) = v ) ) ) ;
hence  contradiction by A2, A3; ::_thesis: verum
end;
then reconsider V2 = V \  {  v where v is Element of V : ( v = v1 or ex c being Chain of G ex vs being FinSequence of the carrier of G st
( not c is empty & vs is_vertex_seq_of c & vs . 1 = v1 & vs . (len vs) = v ) )  }  as non empty set by XBOOLE_0:def_5;
defpred S1[ set ] means ( $1 = v1 or ex c being Chain of G ex vs being FinSequence of the carrier of G st
( not c is empty & vs is_vertex_seq_of c & vs . 1 = v1 & vs . (len vs) = $1 ) );
A4:  {  v where v is Element of V : S1[v]  }  is Subset of V from DOMAIN_1:sch_7();
defpred S2[ set ] means ( the Source of G . $1 in V1 & the Target of G . $1 in V1 );
consider E1 being set  such that
A5: for e being set holds
( e in E1 iff ( e in the carrier' of G & S2[e] ) ) from XBOOLE_0:sch_1();
A6: dom the Source of G = the carrier' of G by FUNCT_2:def_1;
set E2 = the carrier' of G \ E1;
A7: dom ( the Source of G | ( the carrier' of G \ E1)) = (dom the Source of G) /\ ( the carrier' of G \ E1) by RELAT_1:61
.= the carrier' of G \ E1 by A6, XBOOLE_1:28 ;
A8: rng the Source of G c= V by RELAT_1:def_19;
 rng ( the Source of G | ( the carrier' of G \ E1)) c= V2
proof
let v be set ; :: according to TARSKI:def_3 ::_thesis: ( not v in rng ( the Source of G | ( the carrier' of G \ E1)) or v in V2 )
assume  v in rng ( the Source of G | ( the carrier' of G \ E1)) ; ::_thesis: v in V2
then consider e being set  such that
A9: e in dom ( the Source of G | ( the carrier' of G \ E1)) and
A10: ( the Source of G | ( the carrier' of G \ E1)) . e = v by FUNCT_1:def_3;
reconsider e = e as Element of the carrier' of G by A7, A9;
A11: ( the Source of G | ( the carrier' of G \ E1)) . e = the Source of G . e by A9, FUNCT_1:47;
A12: not e in E1 by A7, A9, XBOOLE_0:def_5;
percases ( not e in the carrier' of G or not the Source of G . e in V1 or not the Target of G . e in V1 ) by A5, A12;
suppose not e in the carrier' of G ; ::_thesis: v in V2
hence  v in V2 by A7, A9; ::_thesis: verum
end;
supposeA13: not the Source of G . e in V1 ; ::_thesis: v in V2
 the Source of G . e in V by A7, A9, FUNCT_2:5;
hence  v in V2 by A10, A11, A13, XBOOLE_0:def_5; ::_thesis: verum
end;
supposeA14: not the Target of G . e in V1 ; ::_thesis: v in V2
reconsider Te = the Target of G . e as Vertex of G by A7, A9, FUNCT_2:5;
 ( v in rng ( the Source of G | ( the carrier' of G \ E1)) & rng ( the Source of G | ( the carrier' of G \ E1)) c= rng the Source of G ) by A9, A10, FUNCT_1:def_3, RELAT_1:70;
then A15: v in rng the Source of G ;
assume  not v in V2 ; ::_thesis: contradiction
then  v in V1 by A8, A15, XBOOLE_0:def_5;
then consider v9 being Vertex of G such that
A16: v9 = v and
A17: ( v9 = v1 or ex c being Chain of G ex vs being FinSequence of the carrier of G st
( not c is empty & vs is_vertex_seq_of c & vs . 1 = v1 & vs . (len vs) = v9 ) ) ;
thus  contradiction ::_thesis: verum
proof
percases ( v9 = v1 or ex c being Chain of G ex vs being FinSequence of the carrier of G st
( not c is empty & vs is_vertex_seq_of c & vs . 1 = v1 & vs . (len vs) = v9 ) ) by A17;
supposeA18: v9 = v1 ; ::_thesis: contradiction
reconsider ec = <*e*> as Chain of G by A7, A9, MSSCYC_1:5;
reconsider vs = <*v1,Te*> as FinSequence of the carrier of G ;
 len vs = 2 by FINSEQ_1:44;
then A19: ( vs . 1 = v1 & vs . (len vs) = Te ) by FINSEQ_1:44;
 vs is_vertex_seq_of ec by A10, A11, A16, A18, MSSCYC_1:4;
hence  contradiction by A14, A19; ::_thesis: verum
end;
suppose ex c being Chain of G ex vs being FinSequence of the carrier of G st
( not c is empty & vs is_vertex_seq_of c & vs . 1 = v1 & vs . (len vs) = v9 ) ; ::_thesis: contradiction
then consider c being Chain of G, vs being FinSequence of the carrier of G such that
 not c is empty and
A20: vs is_vertex_seq_of c and
A21: vs . 1 = v1 and
A22: vs . (len vs) = v9 ;
reconsider c9 = c ^ <*e*> as Chain of G by A7, A9, A10, A11, A16, A20, A22, Th12;
 ex vs9 being FinSequence of the carrier of G st
( vs9 = vs ^' <*( the Source of G . e),( the Target of G . e)*> & vs9 is_vertex_seq_of c9 & vs9 . 1 = vs . 1 & vs9 . (len vs9) = Te ) by A7, A9, A10, A11, A16, A20, A22, Th12;
hence  contradiction by A14, A21; ::_thesis: verum
end;
end;
end;
end;
end;
end;
then reconsider S2 = the Source of G | ( the carrier' of G \ E1) as Function of ( the carrier' of G \ E1),V2 by A7, FUNCT_2:def_1, RELSET_1:4;
A23: dom the Target of G = the carrier' of G by FUNCT_2:def_1;
A24: dom ( the Target of G | ( the carrier' of G \ E1)) = (dom the Target of G) /\ ( the carrier' of G \ E1) by RELAT_1:61
.= the carrier' of G \ E1 by A23, XBOOLE_1:28 ;
A25: rng the Target of G c= V by RELAT_1:def_19;
 rng ( the Target of G | ( the carrier' of G \ E1)) c= V2
proof
let v be set ; :: according to TARSKI:def_3 ::_thesis: ( not v in rng ( the Target of G | ( the carrier' of G \ E1)) or v in V2 )
assume  v in rng ( the Target of G | ( the carrier' of G \ E1)) ; ::_thesis: v in V2
then consider e being set  such that
A26: e in dom ( the Target of G | ( the carrier' of G \ E1)) and
A27: ( the Target of G | ( the carrier' of G \ E1)) . e = v by FUNCT_1:def_3;
reconsider e = e as Element of the carrier' of G by A24, A26;
A28: ( the Target of G | ( the carrier' of G \ E1)) . e = the Target of G . e by A26, FUNCT_1:47;
A29: not e in E1 by A24, A26, XBOOLE_0:def_5;
percases ( not e in the carrier' of G or not the Target of G . e in V1 or not the Source of G . e in V1 ) by A5, A29;
suppose not e in the carrier' of G ; ::_thesis: v in V2
hence  v in V2 by A24, A26; ::_thesis: verum
end;
supposeA30: not the Target of G . e in V1 ; ::_thesis: v in V2
 the Target of G . e in V by A24, A26, FUNCT_2:5;
hence  v in V2 by A27, A28, A30, XBOOLE_0:def_5; ::_thesis: verum
end;
supposeA31: not the Source of G . e in V1 ; ::_thesis: v in V2
reconsider Se = the Source of G . e as Vertex of G by A24, A26, FUNCT_2:5;
 ( v in rng ( the Target of G | ( the carrier' of G \ E1)) & rng ( the Target of G | ( the carrier' of G \ E1)) c= rng the Target of G ) by A26, A27, FUNCT_1:def_3, RELAT_1:70;
then A32: v in rng the Target of G ;
assume  not v in V2 ; ::_thesis: contradiction
then  v in V1 by A25, A32, XBOOLE_0:def_5;
then consider v9 being Vertex of G such that
A33: v9 = v and
A34: ( v9 = v1 or ex c being Chain of G ex vs being FinSequence of the carrier of G st
( not c is empty & vs is_vertex_seq_of c & vs . 1 = v1 & vs . (len vs) = v9 ) ) ;
thus  contradiction ::_thesis: verum
proof
percases ( v9 = v1 or ex c being Chain of G ex vs being FinSequence of the carrier of G st
( not c is empty & vs is_vertex_seq_of c & vs . 1 = v1 & vs . (len vs) = v9 ) ) by A34;
supposeA35: v9 = v1 ; ::_thesis: contradiction
reconsider ec = <*e*> as Chain of G by A24, A26, MSSCYC_1:5;
reconsider vs = <*v1,Se*> as FinSequence of the carrier of G ;
 len vs = 2 by FINSEQ_1:44;
then A36: ( vs . 1 = v1 & vs . (len vs) = Se ) by FINSEQ_1:44;
 vs is_vertex_seq_of ec by A27, A28, A33, A35, Th11;
hence  contradiction by A31, A36; ::_thesis: verum
end;
suppose ex c being Chain of G ex vs being FinSequence of the carrier of G st
( not c is empty & vs is_vertex_seq_of c & vs . 1 = v1 & vs . (len vs) = v9 ) ; ::_thesis: contradiction
then consider c being Chain of G, vs being FinSequence of the carrier of G such that
 not c is empty and
A37: vs is_vertex_seq_of c and
A38: vs . 1 = v1 and
A39: vs . (len vs) = v9 ;
reconsider c9 = c ^ <*e*> as Chain of G by A24, A26, A27, A28, A33, A37, A39, Th13;
 ex vs9 being FinSequence of the carrier of G st
( vs9 = vs ^' <*( the Target of G . e),( the Source of G . e)*> & vs9 is_vertex_seq_of c9 & vs9 . 1 = vs . 1 & vs9 . (len vs9) = Se ) by A24, A26, A27, A28, A33, A37, A39, Th13;
hence  contradiction by A31, A38; ::_thesis: verum
end;
end;
end;
end;
end;
end;
then reconsider T2 = the Target of G | ( the carrier' of G \ E1) as Function of ( the carrier' of G \ E1),V2 by A24, FUNCT_2:def_1, RELSET_1:4;
A40: E1 c= the carrier' of G
proof
let e be set ; :: according to TARSKI:def_3 ::_thesis: ( not e in E1 or e in the carrier' of G )
assume  e in E1 ; ::_thesis: e in the carrier' of G
hence  e in the carrier' of G by A5; ::_thesis: verum
end;
A41: dom ( the Target of G | E1) = (dom the Target of G) /\ E1 by RELAT_1:61
.= the carrier' of G /\ E1 by FUNCT_2:def_1
.= E1 by A40, XBOOLE_1:28 ;
 rng ( the Target of G | E1) c= V1
proof
let v be set ; :: according to TARSKI:def_3 ::_thesis: ( not v in rng ( the Target of G | E1) or v in V1 )
assume  v in rng ( the Target of G | E1) ; ::_thesis: v in V1
then consider e being set  such that
A42: e in dom ( the Target of G | E1) and
A43: ( the Target of G | E1) . e = v by FUNCT_1:def_3;
 ( the Target of G | E1) . e = the Target of G . e by A42, FUNCT_1:47;
hence  v in V1 by A5, A41, A42, A43; ::_thesis: verum
end;
then reconsider T1 = the Target of G | E1 as Function of E1,V1 by A41, FUNCT_2:def_1, RELSET_1:4;
A44: dom ( the Source of G | E1) = (dom the Source of G) /\ E1 by RELAT_1:61
.= the carrier' of G /\ E1 by FUNCT_2:def_1
.= E1 by A40, XBOOLE_1:28 ;
 rng ( the Source of G | E1) c= V1
proof
let v be set ; :: according to TARSKI:def_3 ::_thesis: ( not v in rng ( the Source of G | E1) or v in V1 )
assume  v in rng ( the Source of G | E1) ; ::_thesis: v in V1
then consider e being set  such that
A45: e in dom ( the Source of G | E1) and
A46: ( the Source of G | E1) . e = v by FUNCT_1:def_3;
 ( the Source of G | E1) . e = the Source of G . e by A45, FUNCT_1:47;
hence  v in V1 by A5, A44, A45, A46; ::_thesis: verum
end;
then reconsider S1 = the Source of G | E1 as Function of E1,V1 by A44, FUNCT_2:def_1, RELSET_1:4;
reconsider G1 = MultiGraphStruct(# V1,E1,S1,T1 #), G2 = MultiGraphStruct(# V2,( the carrier' of G \ E1),S2,T2 #) as Graph ;
A47: G is_sum_of G1,G2
proof
reconsider MG = MultiGraphStruct(# the carrier of G, the carrier' of G, the Source of G, the Target of G #) as strict Graph ;
thus A48: the Target of G1 tolerates the Target of G2 :: according to GRAPH_1:def_6 ::_thesis: ( the Source of G1 tolerates the Source of G2 & MultiGraphStruct(# the carrier of G, the carrier' of G, the Source of G, the Target of G #) = G1 \/ G2 )
proof
let x be set ; :: according to PARTFUN1:def_4 ::_thesis: ( not x in (dom the Target of G1) /\ (dom the Target of G2) or the Target of G1 . x = the Target of G2 . x )
assume A49: x in (dom the Target of G1) /\ (dom the Target of G2) ; ::_thesis: the Target of G1 . x = the Target of G2 . x
then  x in dom the Target of G2 by XBOOLE_0:def_4;
then A50: x in the carrier' of G \ E1 by FUNCT_2:def_1;
 x in dom the Target of G1 by A49, XBOOLE_0:def_4;
then  x in E1 by FUNCT_2:def_1;
hence  the Target of G1 . x = the Target of G2 . x by A50, XBOOLE_0:def_5; ::_thesis: verum
end;
thus A51: the Source of G1 tolerates the Source of G2 ::_thesis: MultiGraphStruct(# the carrier of G, the carrier' of G, the Source of G, the Target of G #) = G1 \/ G2
proof
let x be set ; :: according to PARTFUN1:def_4 ::_thesis: ( not x in (dom the Source of G1) /\ (dom the Source of G2) or the Source of G1 . x = the Source of G2 . x )
assume A52: x in (dom the Source of G1) /\ (dom the Source of G2) ; ::_thesis: the Source of G1 . x = the Source of G2 . x
then  x in dom the Source of G2 by XBOOLE_0:def_4;
then A53: x in the carrier' of G \ E1 by FUNCT_2:def_1;
 x in dom the Source of G1 by A52, XBOOLE_0:def_4;
then  x in E1 by FUNCT_2:def_1;
hence  the Source of G1 . x = the Source of G2 . x by A53, XBOOLE_0:def_5; ::_thesis: verum
end;
A54: ( ( for v being set st v in the carrier' of G1 holds
( the Source of MG . v = the Source of G1 . v & the Target of MG . v = the Target of G1 . v ) ) & ( for v being set st v in the carrier' of G2 holds
( the Source of MG . v = the Source of G2 . v & the Target of MG . v = the Target of G2 . v ) ) ) by FUNCT_1:49;
 ( the carrier of MG = the carrier of G1 \/ the carrier of G2 & the carrier' of MG = the carrier' of G1 \/ the carrier' of G2 ) by A4, A40, XBOOLE_1:45;
hence  MultiGraphStruct(# the carrier of G, the carrier' of G, the Source of G, the Target of G #) = G1 \/ G2 by A48, A51, A54, GRAPH_1:def_5; ::_thesis: verum
end;
 V1 misses V2 by XBOOLE_1:79;
hence  contradiction by A1, A47, GRAPH_1:def_10; ::_thesis: verum
end;
assume A55: for v1, v2 being Vertex of G st v1 <> v2 holds
ex c being Chain of G ex vs being FinSequence of the carrier of G st
( not c is empty & vs is_vertex_seq_of c & vs . 1 = v1 & vs . (len vs) = v2 ) ; ::_thesis: G is connected
thus  G is connected ::_thesis: verum
proof
given G1, G2 being Graph such that A56: the carrier of G1 misses the carrier of G2 and
A57: G is_sum_of G1,G2 ; :: according to GRAPH_1:def_10 ::_thesis: contradiction
set v2 = the Vertex of G2;
set v1 = the Vertex of G1;
set V2 = the carrier of G2;
set V1 = the carrier of G1;
set T2 = the Target of G2;
set T1 = the Target of G1;
set S2 = the Source of G2;
set S1 = the Source of G1;
set E1 = the carrier' of G1;
A58: MultiGraphStruct(# the carrier of G, the carrier' of G, the Source of G, the Target of G #) = G1 \/ G2 by A57, GRAPH_1:def_6;
A59: ( the Target of G1 tolerates the Target of G2 & the Source of G1 tolerates the Source of G2 ) by A57, GRAPH_1:def_6;
then A60: the carrier' of G = the carrier' of G1 \/ the carrier' of G2 by A58, GRAPH_1:def_5;
 the carrier of MultiGraphStruct(# the carrier of G, the carrier' of G, the Source of G, the Target of G #) = the carrier of G1 \/ the carrier of G2 by A59, A58, GRAPH_1:def_5;
then reconsider v19 = the Vertex of G1, v29 = the Vertex of G2 as Vertex of G by XBOOLE_0:def_3;
A61: the carrier of G1 /\ the carrier of G2 = {} by A56, XBOOLE_0:def_7;
then  the Vertex of G1 <> the Vertex of G2 by XBOOLE_0:def_4;
then consider c being Chain of G, vs being FinSequence of the carrier of G such that
 not c is empty and
A62: vs is_vertex_seq_of c and
A63: vs . 1 = v19 and
A64: vs . (len vs) = v29 by A55;
defpred S1[ Nat] means ( $1 in dom vs & vs . $1 is Vertex of G2 );
A65: len vs = (len c) + 1 by A62, GRAPH_2:def_6;
 c is FinSequence of the carrier' of G by MSSCYC_1:def_1;
then A66: rng c c= the carrier' of G by FINSEQ_1:def_4;
 1 <= (len c) + 1 by NAT_1:11;
then  len vs in dom vs by A65, FINSEQ_3:25;
then A67: ex k being Nat st S1[k] by A64;
consider k being Nat such that
A68: S1[k] and
A69: for n being Nat st S1[n] holds
k <= n from NAT_1:sch_5(A67);
A70: 1 <= k by A68, FINSEQ_3:25;
 k <> 1 by A61, A63, A68, XBOOLE_0:def_4;
then  1 < k by A70, XXREAL_0:1;
then  1 + 1 <= k by NAT_1:13;
then consider i being Element of NAT  such that
A71: 1 <= i and
A72: i < k and
A73: k = i + 1 by GRAPH_2:1;
set e = c . i;
A74: k <= len vs by A68, FINSEQ_3:25;
then A75: i <= len c by A65, A73, XREAL_1:6;
then  i in dom c by A71, FINSEQ_3:25;
then A76: c . i in rng c by FUNCT_1:def_3;
 i <= len vs by A72, A74, XXREAL_0:2;
then A77: i in dom vs by A71, FINSEQ_3:25;
percases ( c . i in the carrier' of G1 or c . i in the carrier' of G2 ) by A60, A66, A76, XBOOLE_0:def_3;
supposeA78: c . i in the carrier' of G1 ; ::_thesis: contradiction
then A79: the Target of G1 . (c . i) in the carrier of G1 by FUNCT_2:5;
A80: the Source of G1 . (c . i) in the carrier of G1 by A78, FUNCT_2:5;
thus  contradiction ::_thesis: verum
proof
percases ( ( vs . i = the Target of G . (c . i) & vs . (i + 1) = the Source of G . (c . i) ) or ( vs . i = the Source of G . (c . i) & vs . (i + 1) = the Target of G . (c . i) ) ) by A62, A71, A75, Lm3;
suppose ( vs . i = the Target of G . (c . i) & vs . (i + 1) = the Source of G . (c . i) ) ; ::_thesis: contradiction
then  vs . k in the carrier of G1 by A59, A58, A73, A78, A80, GRAPH_1:def_5;
hence  contradiction by A61, A68, XBOOLE_0:def_4; ::_thesis: verum
end;
suppose ( vs . i = the Source of G . (c . i) & vs . (i + 1) = the Target of G . (c . i) ) ; ::_thesis: contradiction
then  vs . k in the carrier of G1 by A59, A58, A73, A78, A79, GRAPH_1:def_5;
hence  contradiction by A61, A68, XBOOLE_0:def_4; ::_thesis: verum
end;
end;
end;
end;
supposeA81: c . i in the carrier' of G2 ; ::_thesis: contradiction
then A82: the Target of G2 . (c . i) in the carrier of G2 by FUNCT_2:5;
A83: the Source of G2 . (c . i) in the carrier of G2 by A81, FUNCT_2:5;
thus  contradiction ::_thesis: verum
proof
percases ( ( vs . i = the Target of G . (c . i) & vs . (i + 1) = the Source of G . (c . i) ) or ( vs . i = the Source of G . (c . i) & vs . (i + 1) = the Target of G . (c . i) ) ) by A62, A71, A75, Lm3;
suppose ( vs . i = the Target of G . (c . i) & vs . (i + 1) = the Source of G . (c . i) ) ; ::_thesis: contradiction
then  vs . i in the carrier of G2 by A59, A58, A81, A82, GRAPH_1:def_5;
hence  contradiction by A69, A72, A77; ::_thesis: verum
end;
suppose ( vs . i = the Source of G . (c . i) & vs . (i + 1) = the Target of G . (c . i) ) ; ::_thesis: contradiction
then  vs . i in the carrier of G2 by A59, A58, A81, A83, GRAPH_1:def_5;
hence  contradiction by A69, A72, A77; ::_thesis: verum
end;
end;
end;
end;
end;
end;
end;

theorem Th19: :: GRAPH_3:19
for G being connected Graph
for X being set
for v being Vertex of G st X meets the carrier' of G & not v in G -VSet X holds
ex v9 being Vertex of G ex e being Element of the carrier' of G st
( v9 in G -VSet X & not e in X & ( v9 = the Target of G . e or v9 = the Source of G . e ) )
proof
let G be connected Graph; ::_thesis: for X being set
for v being Vertex of G st X meets the carrier' of G & not v in G -VSet X holds
ex v9 being Vertex of G ex e being Element of the carrier' of G st
( v9 in G -VSet X & not e in X & ( v9 = the Target of G . e or v9 = the Source of G . e ) )
let X be set ; ::_thesis: for v being Vertex of G st X meets the carrier' of G & not v in G -VSet X holds
ex v9 being Vertex of G ex e being Element of the carrier' of G st
( v9 in G -VSet X & not e in X & ( v9 = the Target of G . e or v9 = the Source of G . e ) )
let v be Vertex of G; ::_thesis: ( X meets the carrier' of G & not v in G -VSet X implies ex v9 being Vertex of G ex e being Element of the carrier' of G st
( v9 in G -VSet X & not e in X & ( v9 = the Target of G . e or v9 = the Source of G . e ) ) )
assume that
A1: X meets the carrier' of G and
A2: not v in G -VSet X ; ::_thesis: ex v9 being Vertex of G ex e being Element of the carrier' of G st
( v9 in G -VSet X & not e in X & ( v9 = the Target of G . e or v9 = the Source of G . e ) )
 ex e being set st
( e in X & e in the carrier' of G ) by A1, XBOOLE_0:3;
then  not G -VSet X is empty by Th17;
then consider vv being set  such that
A3: vv in G -VSet X by XBOOLE_0:def_1;
reconsider vv = vv as Vertex of G by A3;
consider c being Chain of G, vs being FinSequence of the carrier of G such that
A4: not c is empty and
A5: vs is_vertex_seq_of c and
A6: vs . 1 = vv and
A7: vs . (len vs) = v by A2, A3, Th18;
defpred S1[ Nat] means ( 1 <= $1 & $1 <= len c & not vs . ($1 + 1) in G -VSet X );
A8: len vs = (len c) + 1 by A5, GRAPH_2:def_6;
 1 + 0 <= len c by A4, NAT_1:13;
then A9: ex n being Nat st S1[n] by A2, A7, A8;
consider k being Nat such that
A10: S1[k] and
A11: for n being Nat st S1[n] holds
k <= n from NAT_1:sch_5(A9);
 len c <= (len c) + 1 by NAT_1:11;
then  k <= len vs by A8, A10, XXREAL_0:2;
then  k in dom vs by A10, FINSEQ_3:25;
then reconsider v9 = vs . k as Vertex of G by FINSEQ_2:11;
reconsider c = c as FinSequence of the carrier' of G by MSSCYC_1:def_1;
A12: rng c c= the carrier' of G by FINSEQ_1:def_4;
 k in dom c by A10, FINSEQ_3:25;
then  c . k in rng c by FUNCT_1:def_3;
then reconsider e = c . k as Element of the carrier' of G by A12;
take  v9 ; ::_thesis: ex e being Element of the carrier' of G st
( v9 in G -VSet X & not e in X & ( v9 = the Target of G . e or v9 = the Source of G . e ) )
take  e ; ::_thesis: ( v9 in G -VSet X & not e in X & ( v9 = the Target of G . e or v9 = the Source of G . e ) )
hereby  ::_thesis: ( not e in X & ( v9 = the Target of G . e or v9 = the Source of G . e ) )
percases ( k = 1 or 1 < k ) by A10, XXREAL_0:1;
suppose k = 1 ; ::_thesis: v9 in G -VSet X
hence  v9 in G -VSet X by A3, A6; ::_thesis: verum
end;
supposeA13: 1 < k ; ::_thesis: v9 in G -VSet X
assume A14: not v9 in G -VSet X ; ::_thesis: contradiction
consider p being Element of NAT  such that
A15: k = 1 + p and
A16: 1 <= p by A13, FINSEQ_4:84;
 p <= k by A15, NAT_1:11;
then  p <= len c by A10, XXREAL_0:2;
then  k <= p by A11, A15, A16, A14;
hence  contradiction by A15, NAT_1:13; ::_thesis: verum
end;
end;
end;
hereby  ::_thesis: ( v9 = the Target of G . e or v9 = the Source of G . e )
 ( 1 <= k + 1 & k + 1 <= len vs ) by A8, A10, NAT_1:11, XREAL_1:6;
then  k + 1 in dom vs by FINSEQ_3:25;
then reconsider v99 = vs . (k + 1) as Vertex of G by FINSEQ_2:11;
assume A17: e in X ; ::_thesis: contradiction
 ( v99 = the Target of G . e or v99 = the Source of G . e ) by A5, A10, Lm3;
hence  contradiction by A10, A17; ::_thesis: verum
end;
thus  ( v9 = the Target of G . e or v9 = the Source of G . e ) by A5, A10, Lm3; ::_thesis: verum
end;

begin

definition
let G be Graph;
let v be Vertex of G;
let X be set ;
func Edges_In (v,X) ->  Subset of the carrier' of G means :Def1: :: GRAPH_3:def 1
 for e being set holds
( e in it iff ( e in the carrier' of G & e in X & the Target of G . e = v ) );
existence
 ex b1 being Subset of the carrier' of G st
for e being set holds
( e in b1 iff ( e in the carrier' of G & e in X & the Target of G . e = v ) )
proof
defpred S1[ set ] means ( $1 in X & the Target of G . $1 = v );
consider IT being set  such that
A1: for x being set holds
( x in IT iff ( x in the carrier' of G & S1[x] ) ) from XBOOLE_0:sch_1();
take  IT ; ::_thesis: ( IT is Subset of the carrier' of G & ( for e being set holds
( e in IT iff ( e in the carrier' of G & e in X & the Target of G . e = v ) ) ) )
 for x being set st x in IT holds
x in the carrier' of G by A1;
hence  IT is Subset of the carrier' of G by TARSKI:def_3; ::_thesis: for e being set holds
( e in IT iff ( e in the carrier' of G & e in X & the Target of G . e = v ) )
thus  for e being set holds
( e in IT iff ( e in the carrier' of G & e in X & the Target of G . e = v ) ) by A1; ::_thesis: verum
end;
uniqueness
 for b1, b2 being Subset of the carrier' of G st ( for e being set holds
( e in b1 iff ( e in the carrier' of G & e in X & the Target of G . e = v ) ) ) & ( for e being set holds
( e in b2 iff ( e in the carrier' of G & e in X & the Target of G . e = v ) ) ) holds
b1 = b2
proof
let it1, it2 be Subset of the carrier' of G; ::_thesis: ( ( for e being set holds
( e in it1 iff ( e in the carrier' of G & e in X & the Target of G . e = v ) ) ) & ( for e being set holds
( e in it2 iff ( e in the carrier' of G & e in X & the Target of G . e = v ) ) ) implies it1 = it2 )
assume that
A2: for e being set holds
( e in it1 iff ( e in the carrier' of G & e in X & the Target of G . e = v ) ) and
A3: for e being set holds
( e in it2 iff ( e in the carrier' of G & e in X & the Target of G . e = v ) ) ; ::_thesis: it1 = it2
now__::_thesis:_for_e_being_set_holds_
(_e_in_it1_iff_e_in_it2_)
let e be set ; ::_thesis: ( e in it1 iff e in it2 )
 ( e in it1 iff ( e in the carrier' of G & e in X & the Target of G . e = v ) ) by A2;
hence  ( e in it1 iff e in it2 ) by A3; ::_thesis: verum
end;
hence  it1 = it2 by TARSKI:1; ::_thesis: verum
end;
func Edges_Out (v,X) ->  Subset of the carrier' of G means :Def2: :: GRAPH_3:def 2
 for e being set holds
( e in it iff ( e in the carrier' of G & e in X & the Source of G . e = v ) );
existence
 ex b1 being Subset of the carrier' of G st
for e being set holds
( e in b1 iff ( e in the carrier' of G & e in X & the Source of G . e = v ) )
proof
defpred S1[ set ] means ( $1 in X & the Source of G . $1 = v );
consider IT being set  such that
A4: for x being set holds
( x in IT iff ( x in the carrier' of G & S1[x] ) ) from XBOOLE_0:sch_1();
take  IT ; ::_thesis: ( IT is Subset of the carrier' of G & ( for e being set holds
( e in IT iff ( e in the carrier' of G & e in X & the Source of G . e = v ) ) ) )
 for x being set st x in IT holds
x in the carrier' of G by A4;
hence  IT is Subset of the carrier' of G by TARSKI:def_3; ::_thesis: for e being set holds
( e in IT iff ( e in the carrier' of G & e in X & the Source of G . e = v ) )
thus  for e being set holds
( e in IT iff ( e in the carrier' of G & e in X & the Source of G . e = v ) ) by A4; ::_thesis: verum
end;
uniqueness
 for b1, b2 being Subset of the carrier' of G st ( for e being set holds
( e in b1 iff ( e in the carrier' of G & e in X & the Source of G . e = v ) ) ) & ( for e being set holds
( e in b2 iff ( e in the carrier' of G & e in X & the Source of G . e = v ) ) ) holds
b1 = b2
proof
let it1, it2 be Subset of the carrier' of G; ::_thesis: ( ( for e being set holds
( e in it1 iff ( e in the carrier' of G & e in X & the Source of G . e = v ) ) ) & ( for e being set holds
( e in it2 iff ( e in the carrier' of G & e in X & the Source of G . e = v ) ) ) implies it1 = it2 )
assume that
A5: for e being set holds
( e in it1 iff ( e in the carrier' of G & e in X & the Source of G . e = v ) ) and
A6: for e being set holds
( e in it2 iff ( e in the carrier' of G & e in X & the Source of G . e = v ) ) ; ::_thesis: it1 = it2
now__::_thesis:_for_e_being_set_holds_
(_e_in_it1_iff_e_in_it2_)
let e be set ; ::_thesis: ( e in it1 iff e in it2 )
 ( e in it1 iff ( e in the carrier' of G & e in X & the Source of G . e = v ) ) by A5;
hence  ( e in it1 iff e in it2 ) by A6; ::_thesis: verum
end;
hence  it1 = it2 by TARSKI:1; ::_thesis: verum
end;
end;

:: deftheorem Def1 defines Edges_In GRAPH_3:def_1_:_
 for G being Graph
for v being Vertex of G
for X being set
for b4 being Subset of the carrier' of G holds
( b4 = Edges_In (v,X) iff for e being set holds
( e in b4 iff ( e in the carrier' of G & e in X & the Target of G . e = v ) ) );

:: deftheorem Def2 defines Edges_Out GRAPH_3:def_2_:_
 for G being Graph
for v being Vertex of G
for X being set
for b4 being Subset of the carrier' of G holds
( b4 = Edges_Out (v,X) iff for e being set holds
( e in b4 iff ( e in the carrier' of G & e in X & the Source of G . e = v ) ) );

definition
let G be Graph;
let v be Vertex of G;
let X be set ;
func Edges_At (v,X) ->  Subset of the carrier' of G equals :: GRAPH_3:def 3
(Edges_In (v,X)) \/ (Edges_Out (v,X));
correctness
coherence
(Edges_In (v,X)) \/ (Edges_Out (v,X)) is Subset of the carrier' of G;
;
end;

:: deftheorem  defines Edges_At GRAPH_3:def_3_:_
 for G being Graph
for v being Vertex of G
for X being set holds Edges_At (v,X) = (Edges_In (v,X)) \/ (Edges_Out (v,X));

registration
let G be finite Graph;
let v be Vertex of G;
let X be set ;
cluster Edges_In (v,X) ->  finite ;
correctness
coherence
Edges_In (v,X) is finite ;
proof
 the carrier' of G is finite by GRAPH_1:def_11;
hence  Edges_In (v,X) is finite ; ::_thesis: verum
end;
cluster Edges_Out (v,X) ->  finite ;
correctness
coherence
Edges_Out (v,X) is finite ;
proof
 the carrier' of G is finite by GRAPH_1:def_11;
hence  Edges_Out (v,X) is finite ; ::_thesis: verum
end;
cluster Edges_At (v,X) ->  finite ;
correctness
coherence
Edges_At (v,X) is finite ;
;
end;

registration
let G be Graph;
let v be Vertex of G;
let X be empty set ;
cluster Edges_In (v,X) ->  empty ;
correctness
coherence
Edges_In (v,X) is empty ;
proof
assume  not Edges_In (v,X) is empty ; ::_thesis: contradiction
then  ex x being set st x in Edges_In (v,X) by XBOOLE_0:def_1;
hence  contradiction by Def1; ::_thesis: verum
end;
cluster Edges_Out (v,X) ->  empty ;
correctness
coherence
Edges_Out (v,X) is empty ;
proof
assume  not Edges_Out (v,X) is empty ; ::_thesis: contradiction
then  ex x being set st x in Edges_Out (v,X) by XBOOLE_0:def_1;
hence  contradiction by Def2; ::_thesis: verum
end;
cluster Edges_At (v,X) ->  empty ;
correctness
coherence
Edges_At (v,X) is empty ;
;
end;

definition
let G be Graph;
let v be Vertex of G;
func Edges_In v ->  Subset of the carrier' of G equals :: GRAPH_3:def 4
 Edges_In (v, the carrier' of G);
correctness
coherence
Edges_In (v, the carrier' of G) is Subset of the carrier' of G;
;
func Edges_Out v ->  Subset of the carrier' of G equals :: GRAPH_3:def 5
 Edges_Out (v, the carrier' of G);
correctness
coherence
Edges_Out (v, the carrier' of G) is Subset of the carrier' of G;
;
end;

:: deftheorem  defines Edges_In GRAPH_3:def_4_:_
 for G being Graph
for v being Vertex of G holds Edges_In v = Edges_In (v, the carrier' of G);

:: deftheorem  defines Edges_Out GRAPH_3:def_5_:_
 for G being Graph
for v being Vertex of G holds Edges_Out v = Edges_Out (v, the carrier' of G);

theorem Th20: :: GRAPH_3:20
for G being Graph
for v being Vertex of G
for X being set holds Edges_In (v,X) c= Edges_In v
proof
let G be Graph; ::_thesis: for v being Vertex of G
for X being set holds Edges_In (v,X) c= Edges_In v
let v be Vertex of G; ::_thesis: for X being set holds Edges_In (v,X) c= Edges_In v
let X be set ; ::_thesis: Edges_In (v,X) c= Edges_In v
let e be set ; :: according to TARSKI:def_3 ::_thesis: ( not e in Edges_In (v,X) or e in Edges_In v )
assume A1: e in Edges_In (v,X) ; ::_thesis: e in Edges_In v
then  the Target of G . e = v by Def1;
hence  e in Edges_In v by A1, Def1; ::_thesis: verum
end;

theorem Th21: :: GRAPH_3:21
for G being Graph
for v being Vertex of G
for X being set holds Edges_Out (v,X) c= Edges_Out v
proof
let G be Graph; ::_thesis: for v being Vertex of G
for X being set holds Edges_Out (v,X) c= Edges_Out v
let v be Vertex of G; ::_thesis: for X being set holds Edges_Out (v,X) c= Edges_Out v
let X be set ; ::_thesis: Edges_Out (v,X) c= Edges_Out v
let e be set ; :: according to TARSKI:def_3 ::_thesis: ( not e in Edges_Out (v,X) or e in Edges_Out v )
assume A1: e in Edges_Out (v,X) ; ::_thesis: e in Edges_Out v
then  the Source of G . e = v by Def2;
hence  e in Edges_Out v by A1, Def2; ::_thesis: verum
end;

registration
let G be finite Graph;
let v be Vertex of G;
cluster Edges_In v ->  finite ;
correctness
coherence
Edges_In v is finite ;
;
cluster Edges_Out v ->  finite ;
correctness
coherence
Edges_Out v is finite ;
;
end;


theorem Th22: :: GRAPH_3:22
for G being finite Graph
for v being Vertex of G holds card (Edges_In v) = EdgesIn v
proof
let G be finite Graph; ::_thesis: for v being Vertex of G holds card (Edges_In v) = EdgesIn v
let v be Vertex of G; ::_thesis: card (Edges_In v) = EdgesIn v
consider X being finite set  such that
A1: for z being set holds
( z in X iff ( z in the carrier' of G & the Target of G . z = v ) ) and
A2: EdgesIn v = card X by GRAPH_1:def_21;
now__::_thesis:_for_e_being_set_holds_
(_e_in_Edges_In_v_iff_e_in_X_)
let e be set ; ::_thesis: ( e in Edges_In v iff e in X )
 ( e in Edges_In (v, the carrier' of G) iff ( e in the carrier' of G & the Target of G . e = v ) ) by Def1;
hence  ( e in Edges_In v iff e in X ) by A1; ::_thesis: verum
end;
hence  card (Edges_In v) = EdgesIn v by A2, TARSKI:1; ::_thesis: verum
end;

theorem Th23: :: GRAPH_3:23
for G being finite Graph
for v being Vertex of G holds card (Edges_Out v) = EdgesOut v
proof
let G be finite Graph; ::_thesis: for v being Vertex of G holds card (Edges_Out v) = EdgesOut v
let v be Vertex of G; ::_thesis: card (Edges_Out v) = EdgesOut v
consider X being finite set  such that
A1: for z being set holds
( z in X iff ( z in the carrier' of G & the Source of G . z = v ) ) and
A2: EdgesOut v = card X by GRAPH_1:def_22;
now__::_thesis:_for_e_being_set_holds_
(_e_in_Edges_Out_v_iff_e_in_X_)
let e be set ; ::_thesis: ( e in Edges_Out v iff e in X )
 ( e in Edges_Out (v, the carrier' of G) iff ( e in the carrier' of G & the Source of G . e = v ) ) by Def2;
hence  ( e in Edges_Out v iff e in X ) by A1; ::_thesis: verum
end;
hence  card (Edges_Out v) = EdgesOut v by A2, TARSKI:1; ::_thesis: verum
end;

definition
let G be finite Graph;
let v be Vertex of G;
let X be set ;
func Degree (v,X) ->  Element of NAT  equals :: GRAPH_3:def 6
(card (Edges_In (v,X))) + (card (Edges_Out (v,X)));
correctness
coherence
(card (Edges_In (v,X))) + (card (Edges_Out (v,X))) is Element of NAT ;
;
end;

:: deftheorem  defines Degree GRAPH_3:def_6_:_
 for G being finite Graph
for v being Vertex of G
for X being set holds Degree (v,X) = (card (Edges_In (v,X))) + (card (Edges_Out (v,X)));

theorem Th24: :: GRAPH_3:24
for G being finite Graph
for v being Vertex of G holds Degree v = Degree (v, the carrier' of G)
proof
let G be finite Graph; ::_thesis: for v being Vertex of G holds Degree v = Degree (v, the carrier' of G)
let v be Vertex of G; ::_thesis: Degree v = Degree (v, the carrier' of G)
thus  Degree v = (card (Edges_In v)) + (EdgesOut v) by Th22
.= (card (Edges_In (v, the carrier' of G))) + (card (Edges_Out v)) by Th23
.= Degree (v, the carrier' of G) ; ::_thesis: verum
end;

theorem Th25: :: GRAPH_3:25
for X being set
for G being finite Graph
for v being Vertex of G st Degree (v,X) <> 0 holds
not Edges_At (v,X) is empty
proof
let X be set ; ::_thesis: for G being finite Graph
for v being Vertex of G st Degree (v,X) <> 0 holds
not Edges_At (v,X) is empty
let G be finite Graph; ::_thesis: for v being Vertex of G st Degree (v,X) <> 0 holds
not Edges_At (v,X) is empty
let v be Vertex of G; ::_thesis: ( Degree (v,X) <> 0 implies not Edges_At (v,X) is empty )
assume A1: Degree (v,X) <> 0 ; ::_thesis: not Edges_At (v,X) is empty
assume A2: Edges_At (v,X) is empty ; ::_thesis: contradiction
then  Edges_In (v,X) = {} ;
hence  contradiction by A1, A2; ::_thesis: verum
end;

theorem Th26: :: GRAPH_3:26
for e, X being set
for G being finite Graph
for v being Vertex of G st e in the carrier' of G & not e in X & ( v = the Target of G . e or v = the Source of G . e ) holds
Degree v <> Degree (v,X)
proof
let e, X be set ; ::_thesis: for G being finite Graph
for v being Vertex of G st e in the carrier' of G & not e in X & ( v = the Target of G . e or v = the Source of G . e ) holds
Degree v <> Degree (v,X)
let G be finite Graph; ::_thesis: for v being Vertex of G st e in the carrier' of G & not e in X & ( v = the Target of G . e or v = the Source of G . e ) holds
Degree v <> Degree (v,X)
let v be Vertex of G; ::_thesis: ( e in the carrier' of G & not e in X & ( v = the Target of G . e or v = the Source of G . e ) implies Degree v <> Degree (v,X) )
set T = the Target of G;
set S = the Source of G;
set E = the carrier' of G;
assume that
A1: e in the carrier' of G and
A2: not e in X and
A3: ( v = the Target of G . e or v = the Source of G . e ) ; ::_thesis: Degree v <> Degree (v,X)
A4: Degree v = Degree (v, the carrier' of G) by Th24;
 Edges_Out v = Edges_Out (v, the carrier' of G) ;
then A5: Edges_Out (v,X) c= Edges_Out (v, the carrier' of G) by Th21;
 Edges_In v = Edges_In (v, the carrier' of G) ;
then A6: Edges_In (v,X) c= Edges_In (v, the carrier' of G) by Th20;
percases ( v = the Target of G . e or v = the Source of G . e ) by A3;
supposeA7: v = the Target of G . e ; ::_thesis: Degree v <> Degree (v,X)
A8: not e in Edges_In (v,X) by A2, Def1;
 e in Edges_In (v, the carrier' of G) by A1, A7, Def1;
then  Edges_In (v,X) c< Edges_In (v, the carrier' of G) by A6, A8, XBOOLE_0:def_8;
then  card (Edges_In (v,X)) < card (Edges_In (v, the carrier' of G)) by CARD_2:48;
hence  Degree v <> Degree (v,X) by A4, A5, NAT_1:43, XREAL_1:8; ::_thesis: verum
end;
supposeA9: v = the Source of G . e ; ::_thesis: Degree v <> Degree (v,X)
A10: not e in Edges_Out (v,X) by A2, Def2;
 e in Edges_Out (v, the carrier' of G) by A1, A9, Def2;
then  Edges_Out (v,X) c< Edges_Out (v, the carrier' of G) by A5, A10, XBOOLE_0:def_8;
then  card (Edges_Out (v,X)) < card (Edges_Out (v, the carrier' of G)) by CARD_2:48;
hence  Degree v <> Degree (v,X) by A4, A6, NAT_1:43, XREAL_1:8; ::_thesis: verum
end;
end;
end;

theorem Th27: :: GRAPH_3:27
for G being finite Graph
for v being Vertex of G
for X2, X1 being set st X2 c= X1 holds
card (Edges_In (v,(X1 \ X2))) = (card (Edges_In (v,X1))) - (card (Edges_In (v,X2)))
proof
let G be finite Graph; ::_thesis: for v being Vertex of G
for X2, X1 being set st X2 c= X1 holds
card (Edges_In (v,(X1 \ X2))) = (card (Edges_In (v,X1))) - (card (Edges_In (v,X2)))
let v be Vertex of G; ::_thesis: for X2, X1 being set st X2 c= X1 holds
card (Edges_In (v,(X1 \ X2))) = (card (Edges_In (v,X1))) - (card (Edges_In (v,X2)))
let X2, X1 be set ; ::_thesis: ( X2 c= X1 implies card (Edges_In (v,(X1 \ X2))) = (card (Edges_In (v,X1))) - (card (Edges_In (v,X2))) )
assume A1: X2 c= X1 ; ::_thesis: card (Edges_In (v,(X1 \ X2))) = (card (Edges_In (v,X1))) - (card (Edges_In (v,X2)))
then A2: X1 = X2 \/ (X1 \ X2) by XBOOLE_1:45;
now__::_thesis:_for_x_being_set_holds_
(_(_x_in_Edges_In_(v,X1)_implies_x_in_(Edges_In_(v,X2))_\/_(Edges_In_(v,(X1_\_X2)))_)_&_(_x_in_(Edges_In_(v,X2))_\/_(Edges_In_(v,(X1_\_X2)))_implies_x_in_Edges_In_(v,X1)_)_)
let x be set ; ::_thesis: ( ( x in Edges_In (v,X1) implies x in (Edges_In (v,X2)) \/ (Edges_In (v,(X1 \ X2))) ) & ( x in (Edges_In (v,X2)) \/ (Edges_In (v,(X1 \ X2))) implies x in Edges_In (v,X1) ) )
hereby  ::_thesis: ( x in (Edges_In (v,X2)) \/ (Edges_In (v,(X1 \ X2))) implies x in Edges_In (v,X1) )
assume A3: x in Edges_In (v,X1) ; ::_thesis: x in (Edges_In (v,X2)) \/ (Edges_In (v,(X1 \ X2)))
then  x in X1 by Def1;
then A4: ( x in X2 or x in X1 \ X2 ) by A2, XBOOLE_0:def_3;
 the Target of G . x = v by A3, Def1;
then  ( x in Edges_In (v,X2) or x in Edges_In (v,(X1 \ X2)) ) by A3, A4, Def1;
hence  x in (Edges_In (v,X2)) \/ (Edges_In (v,(X1 \ X2))) by XBOOLE_0:def_3; ::_thesis: verum
end;
assume A5: x in (Edges_In (v,X2)) \/ (Edges_In (v,(X1 \ X2))) ; ::_thesis: x in Edges_In (v,X1)
then A6: ( x in Edges_In (v,X2) or x in Edges_In (v,(X1 \ X2)) ) by XBOOLE_0:def_3;
then A7: ( x in X2 or x in X1 \ X2 ) by Def1;
 the Target of G . x = v by A6, Def1;
hence  x in Edges_In (v,X1) by A1, A5, A7, Def1; ::_thesis: verum
end;
then A8: Edges_In (v,X1) = (Edges_In (v,X2)) \/ (Edges_In (v,(X1 \ X2))) by TARSKI:1;
 Edges_In (v,X2) misses Edges_In (v,(X1 \ X2))
proof
assume  not Edges_In (v,X2) misses Edges_In (v,(X1 \ X2)) ; ::_thesis: contradiction
then consider x being set  such that
A9: x in (Edges_In (v,X2)) /\ (Edges_In (v,(X1 \ X2))) by XBOOLE_0:4;
 x in Edges_In (v,(X1 \ X2)) by A9, XBOOLE_0:def_4;
then A10: x in X1 \ X2 by Def1;
 x in Edges_In (v,X2) by A9, XBOOLE_0:def_4;
then  x in X2 by Def1;
hence  contradiction by A10, XBOOLE_0:def_5; ::_thesis: verum
end;
then  card (Edges_In (v,X1)) = (card (Edges_In (v,X2))) + (card (Edges_In (v,(X1 \ X2)))) by A8, CARD_2:40;
hence  card (Edges_In (v,(X1 \ X2))) = (card (Edges_In (v,X1))) - (card (Edges_In (v,X2))) ; ::_thesis: verum
end;

theorem Th28: :: GRAPH_3:28
for G being finite Graph
for v being Vertex of G
for X2, X1 being set st X2 c= X1 holds
card (Edges_Out (v,(X1 \ X2))) = (card (Edges_Out (v,X1))) - (card (Edges_Out (v,X2)))
proof
let G be finite Graph; ::_thesis: for v being Vertex of G
for X2, X1 being set st X2 c= X1 holds
card (Edges_Out (v,(X1 \ X2))) = (card (Edges_Out (v,X1))) - (card (Edges_Out (v,X2)))
let v be Vertex of G; ::_thesis: for X2, X1 being set st X2 c= X1 holds
card (Edges_Out (v,(X1 \ X2))) = (card (Edges_Out (v,X1))) - (card (Edges_Out (v,X2)))
let X2, X1 be set ; ::_thesis: ( X2 c= X1 implies card (Edges_Out (v,(X1 \ X2))) = (card (Edges_Out (v,X1))) - (card (Edges_Out (v,X2))) )
assume A1: X2 c= X1 ; ::_thesis: card (Edges_Out (v,(X1 \ X2))) = (card (Edges_Out (v,X1))) - (card (Edges_Out (v,X2)))
then A2: X1 = X2 \/ (X1 \ X2) by XBOOLE_1:45;
now__::_thesis:_for_x_being_set_holds_
(_(_x_in_Edges_Out_(v,X1)_implies_x_in_(Edges_Out_(v,X2))_\/_(Edges_Out_(v,(X1_\_X2)))_)_&_(_x_in_(Edges_Out_(v,X2))_\/_(Edges_Out_(v,(X1_\_X2)))_implies_x_in_Edges_Out_(v,X1)_)_)
let x be set ; ::_thesis: ( ( x in Edges_Out (v,X1) implies x in (Edges_Out (v,X2)) \/ (Edges_Out (v,(X1 \ X2))) ) & ( x in (Edges_Out (v,X2)) \/ (Edges_Out (v,(X1 \ X2))) implies x in Edges_Out (v,X1) ) )
hereby  ::_thesis: ( x in (Edges_Out (v,X2)) \/ (Edges_Out (v,(X1 \ X2))) implies x in Edges_Out (v,X1) )
assume A3: x in Edges_Out (v,X1) ; ::_thesis: x in (Edges_Out (v,X2)) \/ (Edges_Out (v,(X1 \ X2)))
then  x in X1 by Def2;
then A4: ( x in X2 or x in X1 \ X2 ) by A2, XBOOLE_0:def_3;
 the Source of G . x = v by A3, Def2;
then  ( x in Edges_Out (v,X2) or x in Edges_Out (v,(X1 \ X2)) ) by A3, A4, Def2;
hence  x in (Edges_Out (v,X2)) \/ (Edges_Out (v,(X1 \ X2))) by XBOOLE_0:def_3; ::_thesis: verum
end;
assume A5: x in (Edges_Out (v,X2)) \/ (Edges_Out (v,(X1 \ X2))) ; ::_thesis: x in Edges_Out (v,X1)
then A6: ( x in Edges_Out (v,X2) or x in Edges_Out (v,(X1 \ X2)) ) by XBOOLE_0:def_3;
then A7: ( x in X2 or x in X1 \ X2 ) by Def2;
 the Source of G . x = v by A6, Def2;
hence  x in Edges_Out (v,X1) by A1, A5, A7, Def2; ::_thesis: verum
end;
then A8: Edges_Out (v,X1) = (Edges_Out (v,X2)) \/ (Edges_Out (v,(X1 \ X2))) by TARSKI:1;
 Edges_Out (v,X2) misses Edges_Out (v,(X1 \ X2))
proof
assume  not Edges_Out (v,X2) misses Edges_Out (v,(X1 \ X2)) ; ::_thesis: contradiction
then consider x being set  such that
A9: x in (Edges_Out (v,X2)) /\ (Edges_Out (v,(X1 \ X2))) by XBOOLE_0:4;
 x in Edges_Out (v,(X1 \ X2)) by A9, XBOOLE_0:def_4;
then A10: x in X1 \ X2 by Def2;
 x in Edges_Out (v,X2) by A9, XBOOLE_0:def_4;
then  x in X2 by Def2;
hence  contradiction by A10, XBOOLE_0:def_5; ::_thesis: verum
end;
then  card (Edges_Out (v,X1)) = (card (Edges_Out (v,X2))) + (card (Edges_Out (v,(X1 \ X2)))) by A8, CARD_2:40;
hence  card (Edges_Out (v,(X1 \ X2))) = (card (Edges_Out (v,X1))) - (card (Edges_Out (v,X2))) ; ::_thesis: verum
end;

theorem Th29: :: GRAPH_3:29
for G being finite Graph
for v being Vertex of G
for X2, X1 being set st X2 c= X1 holds
Degree (v,(X1 \ X2)) = (Degree (v,X1)) - (Degree (v,X2))
proof
let G be finite Graph; ::_thesis: for v being Vertex of G
for X2, X1 being set st X2 c= X1 holds
Degree (v,(X1 \ X2)) = (Degree (v,X1)) - (Degree (v,X2))
let v be Vertex of G; ::_thesis: for X2, X1 being set st X2 c= X1 holds
Degree (v,(X1 \ X2)) = (Degree (v,X1)) - (Degree (v,X2))
let X2, X1 be set ; ::_thesis: ( X2 c= X1 implies Degree (v,(X1 \ X2)) = (Degree (v,X1)) - (Degree (v,X2)) )
assume  X2 c= X1 ; ::_thesis: Degree (v,(X1 \ X2)) = (Degree (v,X1)) - (Degree (v,X2))
then  ( card (Edges_In (v,(X1 \ X2))) = (card (Edges_In (v,X1))) - (card (Edges_In (v,X2))) & card (Edges_Out (v,(X1 \ X2))) = (card (Edges_Out (v,X1))) - (card (Edges_Out (v,X2))) ) by Th27, Th28;
hence  Degree (v,(X1 \ X2)) = (Degree (v,X1)) - (Degree (v,X2)) ; ::_thesis: verum
end;

theorem Th30: :: GRAPH_3:30
for X being set
for G being finite Graph
for v being Vertex of G holds
( Edges_In (v,X) = Edges_In (v,(X /\ the carrier' of G)) & Edges_Out (v,X) = Edges_Out (v,(X /\ the carrier' of G)) )
proof
let X be set ; ::_thesis: for G being finite Graph
for v being Vertex of G holds
( Edges_In (v,X) = Edges_In (v,(X /\ the carrier' of G)) & Edges_Out (v,X) = Edges_Out (v,(X /\ the carrier' of G)) )
let G be finite Graph; ::_thesis: for v being Vertex of G holds
( Edges_In (v,X) = Edges_In (v,(X /\ the carrier' of G)) & Edges_Out (v,X) = Edges_Out (v,(X /\ the carrier' of G)) )
let v be Vertex of G; ::_thesis: ( Edges_In (v,X) = Edges_In (v,(X /\ the carrier' of G)) & Edges_Out (v,X) = Edges_Out (v,(X /\ the carrier' of G)) )
set E = the carrier' of G;
now__::_thesis:_for_x_being_set_holds_
(_(_x_in_Edges_In_(v,X)_implies_x_in_Edges_In_(v,(X_/\_the_carrier'_of_G))_)_&_(_x_in_Edges_In_(v,(X_/\_the_carrier'_of_G))_implies_x_in_Edges_In_(v,X)_)_)
let x be set ; ::_thesis: ( ( x in Edges_In (v,X) implies x in Edges_In (v,(X /\ the carrier' of G)) ) & ( x in Edges_In (v,(X /\ the carrier' of G)) implies x in Edges_In (v,X) ) )
hereby  ::_thesis: ( x in Edges_In (v,(X /\ the carrier' of G)) implies x in Edges_In (v,X) )
assume A1: x in Edges_In (v,X) ; ::_thesis: x in Edges_In (v,(X /\ the carrier' of G))
then  x in X by Def1;
then A2: x in X /\ the carrier' of G by A1, XBOOLE_0:def_4;
 the Target of G . x = v by A1, Def1;
hence  x in Edges_In (v,(X /\ the carrier' of G)) by A1, A2, Def1; ::_thesis: verum
end;
assume A3: x in Edges_In (v,(X /\ the carrier' of G)) ; ::_thesis: x in Edges_In (v,X)
then  x in X /\ the carrier' of G by Def1;
then A4: x in X by XBOOLE_0:def_4;
 the Target of G . x = v by A3, Def1;
hence  x in Edges_In (v,X) by A3, A4, Def1; ::_thesis: verum
end;
hence  Edges_In (v,X) = Edges_In (v,(X /\ the carrier' of G)) by TARSKI:1; ::_thesis: Edges_Out (v,X) = Edges_Out (v,(X /\ the carrier' of G))
now__::_thesis:_for_x_being_set_holds_
(_(_x_in_Edges_Out_(v,X)_implies_x_in_Edges_Out_(v,(X_/\_the_carrier'_of_G))_)_&_(_x_in_Edges_Out_(v,(X_/\_the_carrier'_of_G))_implies_x_in_Edges_Out_(v,X)_)_)
let x be set ; ::_thesis: ( ( x in Edges_Out (v,X) implies x in Edges_Out (v,(X /\ the carrier' of G)) ) & ( x in Edges_Out (v,(X /\ the carrier' of G)) implies x in Edges_Out (v,X) ) )
hereby  ::_thesis: ( x in Edges_Out (v,(X /\ the carrier' of G)) implies x in Edges_Out (v,X) )
assume A5: x in Edges_Out (v,X) ; ::_thesis: x in Edges_Out (v,(X /\ the carrier' of G))
then  x in X by Def2;
then A6: x in X /\ the carrier' of G by A5, XBOOLE_0:def_4;
 the Source of G . x = v by A5, Def2;
hence  x in Edges_Out (v,(X /\ the carrier' of G)) by A5, A6, Def2; ::_thesis: verum
end;
assume A7: x in Edges_Out (v,(X /\ the carrier' of G)) ; ::_thesis: x in Edges_Out (v,X)
then  x in X /\ the carrier' of G by Def2;
then A8: x in X by XBOOLE_0:def_4;
 the Source of G . x = v by A7, Def2;
hence  x in Edges_Out (v,X) by A7, A8, Def2; ::_thesis: verum
end;
hence  Edges_Out (v,X) = Edges_Out (v,(X /\ the carrier' of G)) by TARSKI:1; ::_thesis: verum
end;

theorem Th31: :: GRAPH_3:31
for X being set
for G being finite Graph
for v being Vertex of G holds Degree (v,X) = Degree (v,(X /\ the carrier' of G))
proof
let X be set ; ::_thesis: for G being finite Graph
for v being Vertex of G holds Degree (v,X) = Degree (v,(X /\ the carrier' of G))
let G be finite Graph; ::_thesis: for v being Vertex of G holds Degree (v,X) = Degree (v,(X /\ the carrier' of G))
let v be Vertex of G; ::_thesis: Degree (v,X) = Degree (v,(X /\ the carrier' of G))
set E = the carrier' of G;
thus  Degree (v,X) = (card (Edges_In (v,(X /\ the carrier' of G)))) + (card (Edges_Out (v,X))) by Th30
.= Degree (v,(X /\ the carrier' of G)) by Th30 ; ::_thesis: verum
end;

theorem Th32: :: GRAPH_3:32
for G being finite Graph
for v being Vertex of G
for c being Chain of G
for vs being FinSequence of the carrier of G st not c is empty & vs is_vertex_seq_of c holds
( v in rng vs iff Degree (v,(rng c)) <> 0 )
proof
let G be finite Graph; ::_thesis: for v being Vertex of G
for c being Chain of G
for vs being FinSequence of the carrier of G st not c is empty & vs is_vertex_seq_of c holds
( v in rng vs iff Degree (v,(rng c)) <> 0 )
let v be Vertex of G; ::_thesis: for c being Chain of G
for vs being FinSequence of the carrier of G st not c is empty & vs is_vertex_seq_of c holds
( v in rng vs iff Degree (v,(rng c)) <> 0 )
let c be Chain of G; ::_thesis: for vs being FinSequence of the carrier of G st not c is empty & vs is_vertex_seq_of c holds
( v in rng vs iff Degree (v,(rng c)) <> 0 )
let vs be FinSequence of the carrier of G; ::_thesis: ( not c is empty & vs is_vertex_seq_of c implies ( v in rng vs iff Degree (v,(rng c)) <> 0 ) )
assume that
A1: not c is empty and
A2: vs is_vertex_seq_of c ; ::_thesis: ( v in rng vs iff Degree (v,(rng c)) <> 0 )
hereby  ::_thesis: ( Degree (v,(rng c)) <> 0 implies v in rng vs )
 c is FinSequence of the carrier' of G by MSSCYC_1:def_1;
then A3: rng c c= the carrier' of G by FINSEQ_1:def_4;
assume that
A4: v in rng vs and
A5: Degree (v,(rng c)) = 0 ; ::_thesis: contradiction
A6: ( Edges_In (v,(rng c)) = {} & Edges_Out (v,(rng c)) = {} ) by A5;
A7: 0 + 1 <= len c by A1, NAT_1:13;
A8: len vs = (len c) + 1 by A2, GRAPH_2:def_6;
consider i being Nat such that
A9: i in dom vs and
A10: vs . i = v by A4, FINSEQ_2:10;
A11: 1 <= i by A9, FINSEQ_3:25;
A12: i <= len vs by A9, FINSEQ_3:25;
percases ( i = len vs or i < len vs ) by A12, XXREAL_0:1;
supposeA13: i = len vs ; ::_thesis: contradiction
set ic = len c;
 len c in dom c by A7, FINSEQ_3:25;
then A14: c . (len c) in rng c by FUNCT_1:def_3;
 ( vs . (len vs) = the Target of G . (c . (len c)) or vs . (len vs) = the Source of G . (c . (len c)) ) by A2, A8, A7, Lm3;
hence  contradiction by A6, A10, A3, A13, A14, Def1, Def2; ::_thesis: verum
end;
suppose i < len vs ; ::_thesis: contradiction
then A15: i <= len c by A8, NAT_1:13;
then  i in dom c by A11, FINSEQ_3:25;
then A16: c . i in rng c by FUNCT_1:def_3;
 ( vs . i = the Target of G . (c . i) or vs . i = the Source of G . (c . i) ) by A2, A11, A15, Lm3;
hence  contradiction by A6, A10, A3, A16, Def1, Def2; ::_thesis: verum
end;
end;
end;
assume that
A17: Degree (v,(rng c)) <> 0 and
A18: not v in rng vs ; ::_thesis: contradiction
percases ( card (Edges_In (v,(rng c))) <> 0 or card (Edges_Out (v,(rng c))) <> 0 ) by A17;
suppose card (Edges_In (v,(rng c))) <> 0 ; ::_thesis: contradiction
then consider e being set  such that
A19: e in Edges_In (v,(rng c)) by CARD_1:27, XBOOLE_0:def_1;
A20: the Target of G . e = v by A19, Def1;
 e in rng c by A19, Def1;
then consider i being Nat such that
A21: i in dom c and
A22: c . i = e by FINSEQ_2:10;
A23: 1 <= i by A21, FINSEQ_3:25;
A24: i <= len c by A21, FINSEQ_3:25;
then  ( 1 <= i + 1 & i + 1 <= len vs ) by A2, A23, Lm3;
then A25: i + 1 in dom vs by FINSEQ_3:25;
 i <= len vs by A2, A23, A24, Lm3;
then A26: i in dom vs by A23, FINSEQ_3:25;
 ( ( vs . i = the Target of G . (c . i) & vs . (i + 1) = the Source of G . (c . i) ) or ( vs . i = the Source of G . (c . i) & vs . (i + 1) = the Target of G . (c . i) ) ) by A2, A23, A24, Lm3;
hence  contradiction by A18, A20, A22, A26, A25, FUNCT_1:def_3; ::_thesis: verum
end;
suppose card (Edges_Out (v,(rng c))) <> 0 ; ::_thesis: contradiction
then consider e being set  such that
A27: e in Edges_Out (v,(rng c)) by CARD_1:27, XBOOLE_0:def_1;
A28: the Source of G . e = v by A27, Def2;
 e in rng c by A27, Def2;
then consider i being Nat such that
A29: i in dom c and
A30: c . i = e by FINSEQ_2:10;
A31: 1 <= i by A29, FINSEQ_3:25;
A32: i <= len c by A29, FINSEQ_3:25;
then  ( 1 <= i + 1 & i + 1 <= len vs ) by A2, A31, Lm3;
then A33: i + 1 in dom vs by FINSEQ_3:25;
 i <= len vs by A2, A31, A32, Lm3;
then A34: i in dom vs by A31, FINSEQ_3:25;
 ( ( vs . i = the Target of G . (c . i) & vs . (i + 1) = the Source of G . (c . i) ) or ( vs . i = the Source of G . (c . i) & vs . (i + 1) = the Target of G . (c . i) ) ) by A2, A31, A32, Lm3;
hence  contradiction by A18, A28, A30, A34, A33, FUNCT_1:def_3; ::_thesis: verum
end;
end;
end;

theorem Th33: :: GRAPH_3:33
for G being non void connected finite Graph
for v being Vertex of G holds Degree v <> 0
proof
let G be non void connected finite Graph; ::_thesis: for v being Vertex of G holds Degree v <> 0
let v be Vertex of G; ::_thesis: Degree v <> 0
assume A1: Degree v = 0 ; ::_thesis: contradiction
set E = the carrier' of G;
A2: Degree v = Degree (v, the carrier' of G) by Th24
.= (card (Edges_In (v, the carrier' of G))) + (card (Edges_Out (v, the carrier' of G))) ;
then A3: Edges_In (v, the carrier' of G) = {} by A1;
A4: Edges_Out (v, the carrier' of G) = {} by A1, A2;
set S = the Source of G;
set T = the Target of G;
consider e being set  such that
A5: e in the carrier' of G by XBOOLE_0:def_1;
reconsider s = the Source of G . e as Vertex of G by A5, FUNCT_2:5;
percases ( v = s or v <> s ) ;
suppose v = s ; ::_thesis: contradiction
hence  contradiction by A4, A5, Def2; ::_thesis: verum
end;
suppose v <> s ; ::_thesis: contradiction
then consider c being Chain of G, vs being FinSequence of the carrier of G such that
A6: not c is empty and
A7: vs is_vertex_seq_of c and
A8: vs . 1 = v and
 vs . (len vs) = s by Th18;
A9: 0 + 1 <= len c by A6, NAT_1:13;
then  1 in dom c by FINSEQ_3:25;
then A10: c . 1 in rng c by FUNCT_1:def_3;
 c is FinSequence of the carrier' of G by MSSCYC_1:def_1;
then A11: rng c c= the carrier' of G by FINSEQ_1:def_4;
 ( vs . 1 = the Target of G . (c . 1) or vs . 1 = the Source of G . (c . 1) ) by A7, A9, Lm3;
hence  contradiction by A3, A4, A8, A11, A10, Def1, Def2; ::_thesis: verum
end;
end;
end;

begin

definition
let G be Graph;
let v1, v2 be Vertex of G;
func AddNewEdge (v1,v2) ->  strict Graph means :Def7: :: GRAPH_3:def 7
( the carrier of it = the carrier of G & the carrier' of it = the carrier' of G \/ { the carrier' of G} & the Source of it = the Source of G +* ( the carrier' of G .--> v1) & the Target of it = the Target of G +* ( the carrier' of G .--> v2) );
existence
 ex b1 being strict Graph st
( the carrier of b1 = the carrier of G & the carrier' of b1 = the carrier' of G \/ { the carrier' of G} & the Source of b1 = the Source of G +* ( the carrier' of G .--> v1) & the Target of b1 = the Target of G +* ( the carrier' of G .--> v2) )
proof
set T = the Target of G;
set E = the carrier' of G;
set V = the carrier of G;
set Eit = the carrier' of G \/ { the carrier' of G};
set t = the carrier' of G .--> v2;
A1: {v1} c= the carrier of G by ZFMISC_1:31;
set Tit = the Target of G +* ( the carrier' of G .--> v2);
A2: dom ( the carrier' of G .--> v2) = { the carrier' of G} by FUNCOP_1:13;
A3: {v2} c= the carrier of G by ZFMISC_1:31;
 ( rng ( the carrier' of G .--> v2) = {v2} & rng the Target of G c= the carrier of G ) by FUNCOP_1:8, RELAT_1:def_19;
then  ( rng ( the Target of G +* ( the carrier' of G .--> v2)) c= (rng the Target of G) \/ (rng ( the carrier' of G .--> v2)) & (rng the Target of G) \/ (rng ( the carrier' of G .--> v2)) c= the carrier of G ) by A3, FUNCT_4:17, XBOOLE_1:8;
then A4: rng ( the Target of G +* ( the carrier' of G .--> v2)) c= the carrier of G by XBOOLE_1:1;
dom ( the Target of G +* ( the carrier' of G .--> v2)) = (dom the Target of G) \/ (dom ( the carrier' of G .--> v2)) by FUNCT_4:def_1
.= the carrier' of G \/ { the carrier' of G} by A2, FUNCT_2:def_1 ;
then reconsider Tit = the Target of G +* ( the carrier' of G .--> v2) as Function of ( the carrier' of G \/ { the carrier' of G}), the carrier of G by A4, FUNCT_2:def_1, RELSET_1:4;
set S = the Source of G;
set s = the carrier' of G .--> v1;
A5: dom ( the carrier' of G .--> v1) = { the carrier' of G} by FUNCOP_1:13;
set Sit = the Source of G +* ( the carrier' of G .--> v1);
A6: dom ( the Source of G +* ( the carrier' of G .--> v1)) = (dom the Source of G) \/ (dom ( the carrier' of G .--> v1)) by FUNCT_4:def_1
.= the carrier' of G \/ { the carrier' of G} by A5, FUNCT_2:def_1 ;
 ( rng ( the carrier' of G .--> v1) = {v1} & rng the Source of G c= the carrier of G ) by FUNCOP_1:8, RELAT_1:def_19;
then  ( rng ( the Source of G +* ( the carrier' of G .--> v1)) c= (rng the Source of G) \/ (rng ( the carrier' of G .--> v1)) & (rng the Source of G) \/ (rng ( the carrier' of G .--> v1)) c= the carrier of G ) by A1, FUNCT_4:17, XBOOLE_1:8;
then  rng ( the Source of G +* ( the carrier' of G .--> v1)) c= the carrier of G by XBOOLE_1:1;
then reconsider Sit = the Source of G +* ( the carrier' of G .--> v1) as Function of ( the carrier' of G \/ { the carrier' of G}), the carrier of G by A6, FUNCT_2:def_1, RELSET_1:4;
reconsider IT = MultiGraphStruct(# the carrier of G,( the carrier' of G \/ { the carrier' of G}),Sit,Tit #) as non empty strict MultiGraphStruct ;
take  IT ; ::_thesis: ( the carrier of IT = the carrier of G & the carrier' of IT = the carrier' of G \/ { the carrier' of G} & the Source of IT = the Source of G +* ( the carrier' of G .--> v1) & the Target of IT = the Target of G +* ( the carrier' of G .--> v2) )
thus  ( the carrier of IT = the carrier of G & the carrier' of IT = the carrier' of G \/ { the carrier' of G} & the Source of IT = the Source of G +* ( the carrier' of G .--> v1) & the Target of IT = the Target of G +* ( the carrier' of G .--> v2) ) ; ::_thesis: verum
end;
uniqueness
 for b1, b2 being strict Graph st the carrier of b1 = the carrier of G & the carrier' of b1 = the carrier' of G \/ { the carrier' of G} & the Source of b1 = the Source of G +* ( the carrier' of G .--> v1) & the Target of b1 = the Target of G +* ( the carrier' of G .--> v2) & the carrier of b2 = the carrier of G & the carrier' of b2 = the carrier' of G \/ { the carrier' of G} & the Source of b2 = the Source of G +* ( the carrier' of G .--> v1) & the Target of b2 = the Target of G +* ( the carrier' of G .--> v2) holds
b1 = b2 ;
end;

:: deftheorem Def7 defines AddNewEdge GRAPH_3:def_7_:_
 for G being Graph
for v1, v2 being Vertex of G
for b4 being strict Graph holds
( b4 = AddNewEdge (v1,v2) iff ( the carrier of b4 = the carrier of G & the carrier' of b4 = the carrier' of G \/ { the carrier' of G} & the Source of b4 = the Source of G +* ( the carrier' of G .--> v1) & the Target of b4 = the Target of G +* ( the carrier' of G .--> v2) ) );

registration
let G be finite Graph;
let v1, v2 be Vertex of G;
cluster AddNewEdge (v1,v2) ->  strict finite ;
coherence
 AddNewEdge (v1,v2) is finite
proof
reconsider E = the carrier' of G as finite set by GRAPH_1:def_11;
reconsider V = the carrier of G as finite set by GRAPH_1:def_11;
 the carrier of (AddNewEdge (v1,v2)) = V by Def7;
hence  the carrier of (AddNewEdge (v1,v2)) is finite ; :: according to GRAPH_1:def_11 ::_thesis: the carrier' of (AddNewEdge (v1,v2)) is finite
 the carrier' of (AddNewEdge (v1,v2)) = E \/ { the carrier' of G} by Def7;
hence  the carrier' of (AddNewEdge (v1,v2)) is finite ; ::_thesis: verum
end;
end;


theorem Th34: :: GRAPH_3:34
for G being Graph
for v1, v2 being Vertex of G holds
( the carrier' of G in the carrier' of (AddNewEdge (v1,v2)) & the carrier' of G = the carrier' of (AddNewEdge (v1,v2)) \ { the carrier' of G} & the Source of (AddNewEdge (v1,v2)) . the carrier' of G = v1 & the Target of (AddNewEdge (v1,v2)) . the carrier' of G = v2 )
proof
let G be Graph; ::_thesis: for v1, v2 being Vertex of G holds
( the carrier' of G in the carrier' of (AddNewEdge (v1,v2)) & the carrier' of G = the carrier' of (AddNewEdge (v1,v2)) \ { the carrier' of G} & the Source of (AddNewEdge (v1,v2)) . the carrier' of G = v1 & the Target of (AddNewEdge (v1,v2)) . the carrier' of G = v2 )
let v1, v2 be Vertex of G; ::_thesis: ( the carrier' of G in the carrier' of (AddNewEdge (v1,v2)) & the carrier' of G = the carrier' of (AddNewEdge (v1,v2)) \ { the carrier' of G} & the Source of (AddNewEdge (v1,v2)) . the carrier' of G = v1 & the Target of (AddNewEdge (v1,v2)) . the carrier' of G = v2 )
set G9 = AddNewEdge (v1,v2);
set E = the carrier' of G;
set S = the Source of G;
set T = the Target of G;
set E9 = the carrier' of (AddNewEdge (v1,v2));
A1: the carrier' of (AddNewEdge (v1,v2)) = the carrier' of G \/ { the carrier' of G} by Def7;
 the carrier' of G in { the carrier' of G} by TARSKI:def_1;
hence  the carrier' of G in the carrier' of (AddNewEdge (v1,v2)) by A1, XBOOLE_0:def_3; ::_thesis: ( the carrier' of G = the carrier' of (AddNewEdge (v1,v2)) \ { the carrier' of G} & the Source of (AddNewEdge (v1,v2)) . the carrier' of G = v1 & the Target of (AddNewEdge (v1,v2)) . the carrier' of G = v2 )
now__::_thesis:_for_x_being_set_holds_
(_(_x_in_the_carrier'_of_G_implies_x_in_the_carrier'_of_(AddNewEdge_(v1,v2))_\_{_the_carrier'_of_G}_)_&_(_x_in_the_carrier'_of_(AddNewEdge_(v1,v2))_\_{_the_carrier'_of_G}_implies_x_in_the_carrier'_of_G_)_)
let x be set ; ::_thesis: ( ( x in the carrier' of G implies x in the carrier' of (AddNewEdge (v1,v2)) \ { the carrier' of G} ) & ( x in the carrier' of (AddNewEdge (v1,v2)) \ { the carrier' of G} implies x in the carrier' of G ) )
hereby  ::_thesis: ( x in the carrier' of (AddNewEdge (v1,v2)) \ { the carrier' of G} implies x in the carrier' of G )
assume A2: x in the carrier' of G ; ::_thesis: x in the carrier' of (AddNewEdge (v1,v2)) \ { the carrier' of G}
then  x <> the carrier' of G ;
then A3: not x in { the carrier' of G} by TARSKI:def_1;
 x in the carrier' of (AddNewEdge (v1,v2)) by A1, A2, XBOOLE_0:def_3;
hence  x in the carrier' of (AddNewEdge (v1,v2)) \ { the carrier' of G} by A3, XBOOLE_0:def_5; ::_thesis: verum
end;
assume A4: x in the carrier' of (AddNewEdge (v1,v2)) \ { the carrier' of G} ; ::_thesis: x in the carrier' of G
then  not x in { the carrier' of G} by XBOOLE_0:def_5;
hence  x in the carrier' of G by A1, A4, XBOOLE_0:def_3; ::_thesis: verum
end;
hence  the carrier' of G = the carrier' of (AddNewEdge (v1,v2)) \ { the carrier' of G} by TARSKI:1; ::_thesis: ( the Source of (AddNewEdge (v1,v2)) . the carrier' of G = v1 & the Target of (AddNewEdge (v1,v2)) . the carrier' of G = v2 )
 dom ( the carrier' of G .--> v1) = { the carrier' of G} by FUNCOP_1:13;
then A5: the carrier' of G in dom ( the carrier' of G .--> v1) by TARSKI:def_1;
 the Source of (AddNewEdge (v1,v2)) = the Source of G +* ( the carrier' of G .--> v1) by Def7;
hence  the Source of (AddNewEdge (v1,v2)) . the carrier' of G = ( the carrier' of G .--> v1) . the carrier' of G by A5, FUNCT_4:13
.= v1 by FUNCOP_1:72 ;
::_thesis: the Target of (AddNewEdge (v1,v2)) . the carrier' of G = v2
 dom ( the carrier' of G .--> v2) = { the carrier' of G} by FUNCOP_1:13;
then A6: the carrier' of G in dom ( the carrier' of G .--> v2) by TARSKI:def_1;
 the Target of (AddNewEdge (v1,v2)) = the Target of G +* ( the carrier' of G .--> v2) by Def7;
hence  the Target of (AddNewEdge (v1,v2)) . the carrier' of G = ( the carrier' of G .--> v2) . the carrier' of G by A6, FUNCT_4:13
.= v2 by FUNCOP_1:72 ;
::_thesis: verum
end;

theorem Th35: :: GRAPH_3:35
for e being set
for G being Graph
for v1, v2 being Vertex of G st e in the carrier' of G holds
( the Source of (AddNewEdge (v1,v2)) . e = the Source of G . e & the Target of (AddNewEdge (v1,v2)) . e = the Target of G . e )
proof
let e be set ; ::_thesis: for G being Graph
for v1, v2 being Vertex of G st e in the carrier' of G holds
( the Source of (AddNewEdge (v1,v2)) . e = the Source of G . e & the Target of (AddNewEdge (v1,v2)) . e = the Target of G . e )
let G be Graph; ::_thesis: for v1, v2 being Vertex of G st e in the carrier' of G holds
( the Source of (AddNewEdge (v1,v2)) . e = the Source of G . e & the Target of (AddNewEdge (v1,v2)) . e = the Target of G . e )
let v1, v2 be Vertex of G; ::_thesis: ( e in the carrier' of G implies ( the Source of (AddNewEdge (v1,v2)) . e = the Source of G . e & the Target of (AddNewEdge (v1,v2)) . e = the Target of G . e ) )
set S = the Source of G;
set T = the Target of G;
set E = the carrier' of G;
set G9 = AddNewEdge (v1,v2);
set S9 = the Source of (AddNewEdge (v1,v2));
set T9 = the Target of (AddNewEdge (v1,v2));
assume A1: e in the carrier' of G ; ::_thesis: ( the Source of (AddNewEdge (v1,v2)) . e = the Source of G . e & the Target of (AddNewEdge (v1,v2)) . e = the Target of G . e )
A2: not e in dom ( the carrier' of G .--> v1)
proof
assume  e in dom ( the carrier' of G .--> v1) ; ::_thesis: contradiction
then  e in { the carrier' of G} by FUNCOP_1:13;
then  e = the carrier' of G by TARSKI:def_1;
hence  contradiction by A1; ::_thesis: verum
end;
thus  the Source of (AddNewEdge (v1,v2)) . e = ( the Source of G +* ( the carrier' of G .--> v1)) . e by Def7
.= the Source of G . e by A2, FUNCT_4:11 ; ::_thesis: the Target of (AddNewEdge (v1,v2)) . e = the Target of G . e
A3: not e in dom ( the carrier' of G .--> v2)
proof
assume  e in dom ( the carrier' of G .--> v2) ; ::_thesis: contradiction
then  e in { the carrier' of G} by FUNCOP_1:13;
then  e = the carrier' of G by TARSKI:def_1;
hence  contradiction by A1; ::_thesis: verum
end;
thus  the Target of (AddNewEdge (v1,v2)) . e = ( the Target of G +* ( the carrier' of G .--> v2)) . e by Def7
.= the Target of G . e by A3, FUNCT_4:11 ; ::_thesis: verum
end;

theorem Th36: :: GRAPH_3:36
for G being Graph
for v1, v2 being Vertex of G
for c being Chain of G
for vs being FinSequence of the carrier of G
for vs9 being FinSequence of the carrier of (AddNewEdge (v1,v2)) st vs9 = vs & vs is_vertex_seq_of c holds
vs9 is_vertex_seq_of c
proof
let G be Graph; ::_thesis: for v1, v2 being Vertex of G
for c being Chain of G
for vs being FinSequence of the carrier of G
for vs9 being FinSequence of the carrier of (AddNewEdge (v1,v2)) st vs9 = vs & vs is_vertex_seq_of c holds
vs9 is_vertex_seq_of c
let v1, v2 be Vertex of G; ::_thesis: for c being Chain of G
for vs being FinSequence of the carrier of G
for vs9 being FinSequence of the carrier of (AddNewEdge (v1,v2)) st vs9 = vs & vs is_vertex_seq_of c holds
vs9 is_vertex_seq_of c
let c be Chain of G; ::_thesis: for vs being FinSequence of the carrier of G
for vs9 being FinSequence of the carrier of (AddNewEdge (v1,v2)) st vs9 = vs & vs is_vertex_seq_of c holds
vs9 is_vertex_seq_of c
let vs be FinSequence of the carrier of G; ::_thesis: for vs9 being FinSequence of the carrier of (AddNewEdge (v1,v2)) st vs9 = vs & vs is_vertex_seq_of c holds
vs9 is_vertex_seq_of c
let vs9 be FinSequence of the carrier of (AddNewEdge (v1,v2)); ::_thesis: ( vs9 = vs & vs is_vertex_seq_of c implies vs9 is_vertex_seq_of c )
assume that
A1: vs9 = vs and
A2: vs is_vertex_seq_of c ; ::_thesis: vs9 is_vertex_seq_of c
thus  len vs9 = (len c) + 1 by A1, A2, GRAPH_2:def_6; :: according to GRAPH_2:def_6 ::_thesis: for b1 being Element of NAT holds
( not 1 <= b1 or not b1 <= len c or c . b1 joins vs9 /. b1,vs9 /. (b1 + 1) )
let n be Element of NAT ; ::_thesis: ( not 1 <= n or not n <= len c or c . n joins vs9 /. n,vs9 /. (n + 1) )
set T = the Target of G;
set S = the Source of G;
set v = c . n;
set x = vs /. n;
set y = vs /. (n + 1);
assume A3: ( 1 <= n & n <= len c ) ; ::_thesis: c . n joins vs9 /. n,vs9 /. (n + 1)
then  c . n joins vs /. n,vs /. (n + 1) by A2, GRAPH_2:def_6;
then A4: ( ( the Source of G . (c . n) = vs /. n & the Target of G . (c . n) = vs /. (n + 1) ) or ( the Source of G . (c . n) = vs /. (n + 1) & the Target of G . (c . n) = vs /. n ) ) by GRAPH_1:def_12;
set G9 = AddNewEdge (v1,v2);
set S9 = the Source of (AddNewEdge (v1,v2));
set T9 = the Target of (AddNewEdge (v1,v2));
A5: the carrier of G = the carrier of (AddNewEdge (v1,v2)) by Def7;
 c is FinSequence of the carrier' of G by MSSCYC_1:def_1;
then A6: rng c c= the carrier' of G by FINSEQ_1:def_4;
 n in dom c by A3, FINSEQ_3:25;
then  c . n in rng c by FUNCT_1:def_3;
then  ( the Source of (AddNewEdge (v1,v2)) . (c . n) = the Source of G . (c . n) & the Target of G . (c . n) = the Target of (AddNewEdge (v1,v2)) . (c . n) ) by A6, Th35;
hence  c . n joins vs9 /. n,vs9 /. (n + 1) by A1, A5, A4, GRAPH_1:def_12; ::_thesis: verum
end;

theorem Th37: :: GRAPH_3:37
for G being Graph
for v1, v2 being Vertex of G
for c being Chain of G holds c is Chain of AddNewEdge (v1,v2)
proof
let G be Graph; ::_thesis: for v1, v2 being Vertex of G
for c being Chain of G holds c is Chain of AddNewEdge (v1,v2)
let v1, v2 be Vertex of G; ::_thesis: for c being Chain of G holds c is Chain of AddNewEdge (v1,v2)
let c be Chain of G; ::_thesis: c is Chain of AddNewEdge (v1,v2)
set G9 = AddNewEdge (v1,v2);
consider p being FinSequence of the carrier of G such that
A1: p is_vertex_seq_of c by GRAPH_2:33;
 c is FinSequence of the carrier' of G by MSSCYC_1:def_1;
then A2: rng c c= the carrier' of G by FINSEQ_1:def_4;
 the carrier' of (AddNewEdge (v1,v2)) = the carrier' of G \/ { the carrier' of G} by Def7;
then  the carrier' of G c= the carrier' of (AddNewEdge (v1,v2)) by XBOOLE_1:7;
then  rng c c= the carrier' of (AddNewEdge (v1,v2)) by A2, XBOOLE_1:1;
hence  c is FinSequence of the carrier' of (AddNewEdge (v1,v2)) by FINSEQ_1:def_4; :: according to MSSCYC_1:def_1 ::_thesis: ex b1 being FinSequence of the carrier of (AddNewEdge (v1,v2)) st b1 is_vertex_seq_of c
reconsider p9 = p as FinSequence of the carrier of (AddNewEdge (v1,v2)) by Def7;
take  p9 ; ::_thesis: p9 is_vertex_seq_of c
thus  p9 is_vertex_seq_of c by A1, Th36; ::_thesis: verum
end;

theorem :: GRAPH_3:38
for G being Graph
for v1, v2 being Vertex of G
for p being Path of G holds p is Path of AddNewEdge (v1,v2) by Th37;

theorem Th39: :: GRAPH_3:39
for X being set
for G being Graph
for v1, v2 being Vertex of G
for v9 being Vertex of (AddNewEdge (v1,v2)) st v9 = v1 & v1 <> v2 holds
Edges_In (v9,X) = Edges_In (v1,X)
proof
let X be set ; ::_thesis: for G being Graph
for v1, v2 being Vertex of G
for v9 being Vertex of (AddNewEdge (v1,v2)) st v9 = v1 & v1 <> v2 holds
Edges_In (v9,X) = Edges_In (v1,X)
let G be Graph; ::_thesis: for v1, v2 being Vertex of G
for v9 being Vertex of (AddNewEdge (v1,v2)) st v9 = v1 & v1 <> v2 holds
Edges_In (v9,X) = Edges_In (v1,X)
let v1, v2 be Vertex of G; ::_thesis: for v9 being Vertex of (AddNewEdge (v1,v2)) st v9 = v1 & v1 <> v2 holds
Edges_In (v9,X) = Edges_In (v1,X)
let v9 be Vertex of (AddNewEdge (v1,v2)); ::_thesis: ( v9 = v1 & v1 <> v2 implies Edges_In (v9,X) = Edges_In (v1,X) )
assume that
A1: v9 = v1 and
A2: v1 <> v2 ; ::_thesis: Edges_In (v9,X) = Edges_In (v1,X)
set G9 = AddNewEdge (v1,v2);
set E = the carrier' of G;
set T = the Target of G;
set E9 = the carrier' of (AddNewEdge (v1,v2));
set T9 = the Target of (AddNewEdge (v1,v2));
A3: the carrier' of (AddNewEdge (v1,v2)) = the carrier' of G \/ { the carrier' of G} by Def7;
now__::_thesis:_for_x_being_set_holds_
(_(_x_in_Edges_In_(v9,X)_implies_x_in_Edges_In_(v1,X)_)_&_(_x_in_Edges_In_(v1,X)_implies_x_in_Edges_In_(v9,X)_)_)
let x be set ; ::_thesis: ( ( x in Edges_In (v9,X) implies x in Edges_In (v1,X) ) & ( x in Edges_In (v1,X) implies x in Edges_In (v9,X) ) )
hereby  ::_thesis: ( x in Edges_In (v1,X) implies x in Edges_In (v9,X) )
assume A4: x in Edges_In (v9,X) ; ::_thesis: x in Edges_In (v1,X)
then A5: x in X by Def1;
A6: the Target of (AddNewEdge (v1,v2)) . x = v9 by A4, Def1;
 the Target of (AddNewEdge (v1,v2)) . the carrier' of G = v2 by Th34;
then  not x in { the carrier' of G} by A1, A2, A6, TARSKI:def_1;
then A7: x in the carrier' of G by A3, A4, XBOOLE_0:def_3;
then  the Target of G . x = v1 by A1, A6, Th35;
hence  x in Edges_In (v1,X) by A5, A7, Def1; ::_thesis: verum
end;
assume A8: x in Edges_In (v1,X) ; ::_thesis: x in Edges_In (v9,X)
then  the Target of G . x = v1 by Def1;
then A9: the Target of (AddNewEdge (v1,v2)) . x = v9 by A1, A8, Th35;
 ( x in X & x in the carrier' of (AddNewEdge (v1,v2)) ) by A3, A8, Def1, XBOOLE_0:def_3;
hence  x in Edges_In (v9,X) by A9, Def1; ::_thesis: verum
end;
hence  Edges_In (v9,X) = Edges_In (v1,X) by TARSKI:1; ::_thesis: verum
end;

theorem Th40: :: GRAPH_3:40
for X being set
for G being Graph
for v2, v1 being Vertex of G
for v9 being Vertex of (AddNewEdge (v1,v2)) st v9 = v2 & v1 <> v2 holds
Edges_Out (v9,X) = Edges_Out (v2,X)
proof
let X be set ; ::_thesis: for G being Graph
for v2, v1 being Vertex of G
for v9 being Vertex of (AddNewEdge (v1,v2)) st v9 = v2 & v1 <> v2 holds
Edges_Out (v9,X) = Edges_Out (v2,X)
let G be Graph; ::_thesis: for v2, v1 being Vertex of G
for v9 being Vertex of (AddNewEdge (v1,v2)) st v9 = v2 & v1 <> v2 holds
Edges_Out (v9,X) = Edges_Out (v2,X)
let v2, v1 be Vertex of G; ::_thesis: for v9 being Vertex of (AddNewEdge (v1,v2)) st v9 = v2 & v1 <> v2 holds
Edges_Out (v9,X) = Edges_Out (v2,X)
let v9 be Vertex of (AddNewEdge (v1,v2)); ::_thesis: ( v9 = v2 & v1 <> v2 implies Edges_Out (v9,X) = Edges_Out (v2,X) )
assume that
A1: v9 = v2 and
A2: v1 <> v2 ; ::_thesis: Edges_Out (v9,X) = Edges_Out (v2,X)
set G9 = AddNewEdge (v1,v2);
set E = the carrier' of G;
set S = the Source of G;
set E9 = the carrier' of (AddNewEdge (v1,v2));
set S9 = the Source of (AddNewEdge (v1,v2));
A3: the carrier' of (AddNewEdge (v1,v2)) = the carrier' of G \/ { the carrier' of G} by Def7;
now__::_thesis:_for_x_being_set_holds_
(_(_x_in_Edges_Out_(v9,X)_implies_x_in_Edges_Out_(v2,X)_)_&_(_x_in_Edges_Out_(v2,X)_implies_x_in_Edges_Out_(v9,X)_)_)
let x be set ; ::_thesis: ( ( x in Edges_Out (v9,X) implies x in Edges_Out (v2,X) ) & ( x in Edges_Out (v2,X) implies x in Edges_Out (v9,X) ) )
hereby  ::_thesis: ( x in Edges_Out (v2,X) implies x in Edges_Out (v9,X) )
assume A4: x in Edges_Out (v9,X) ; ::_thesis: x in Edges_Out (v2,X)
then A5: x in X by Def2;
A6: the Source of (AddNewEdge (v1,v2)) . x = v9 by A4, Def2;
 the Source of (AddNewEdge (v1,v2)) . the carrier' of G = v1 by Th34;
then  not x in { the carrier' of G} by A1, A2, A6, TARSKI:def_1;
then A7: x in the carrier' of G by A3, A4, XBOOLE_0:def_3;
then  the Source of G . x = v2 by A1, A6, Th35;
hence  x in Edges_Out (v2,X) by A5, A7, Def2; ::_thesis: verum
end;
assume A8: x in Edges_Out (v2,X) ; ::_thesis: x in Edges_Out (v9,X)
then  the Source of G . x = v2 by Def2;
then A9: the Source of (AddNewEdge (v1,v2)) . x = v9 by A1, A8, Th35;
 ( x in X & x in the carrier' of (AddNewEdge (v1,v2)) ) by A3, A8, Def2, XBOOLE_0:def_3;
hence  x in Edges_Out (v9,X) by A9, Def2; ::_thesis: verum
end;
hence  Edges_Out (v9,X) = Edges_Out (v2,X) by TARSKI:1; ::_thesis: verum
end;

theorem Th41: :: GRAPH_3:41
for X being set
for G being Graph
for v2, v1 being Vertex of G
for v9 being Vertex of (AddNewEdge (v1,v2)) st v9 = v1 & the carrier' of G in X holds
( Edges_Out (v9,X) = (Edges_Out (v1,X)) \/ { the carrier' of G} & Edges_Out (v1,X) misses { the carrier' of G} )
proof
let X be set ; ::_thesis: for G being Graph
for v2, v1 being Vertex of G
for v9 being Vertex of (AddNewEdge (v1,v2)) st v9 = v1 & the carrier' of G in X holds
( Edges_Out (v9,X) = (Edges_Out (v1,X)) \/ { the carrier' of G} & Edges_Out (v1,X) misses { the carrier' of G} )
let G be Graph; ::_thesis: for v2, v1 being Vertex of G
for v9 being Vertex of (AddNewEdge (v1,v2)) st v9 = v1 & the carrier' of G in X holds
( Edges_Out (v9,X) = (Edges_Out (v1,X)) \/ { the carrier' of G} & Edges_Out (v1,X) misses { the carrier' of G} )
let v2, v1 be Vertex of G; ::_thesis: for v9 being Vertex of (AddNewEdge (v1,v2)) st v9 = v1 & the carrier' of G in X holds
( Edges_Out (v9,X) = (Edges_Out (v1,X)) \/ { the carrier' of G} & Edges_Out (v1,X) misses { the carrier' of G} )
let v9 be Vertex of (AddNewEdge (v1,v2)); ::_thesis: ( v9 = v1 & the carrier' of G in X implies ( Edges_Out (v9,X) = (Edges_Out (v1,X)) \/ { the carrier' of G} & Edges_Out (v1,X) misses { the carrier' of G} ) )
assume that
A1: v9 = v1 and
A2: the carrier' of G in X ; ::_thesis: ( Edges_Out (v9,X) = (Edges_Out (v1,X)) \/ { the carrier' of G} & Edges_Out (v1,X) misses { the carrier' of G} )
set G9 = AddNewEdge (v1,v2);
set E = the carrier' of G;
set S = the Source of G;
set E9 = the carrier' of (AddNewEdge (v1,v2));
set S9 = the Source of (AddNewEdge (v1,v2));
A3: the carrier' of (AddNewEdge (v1,v2)) = the carrier' of G \/ { the carrier' of G} by Def7;
now__::_thesis:_for_x_being_set_holds_
(_(_x_in_Edges_Out_(v9,X)_implies_x_in_(Edges_Out_(v1,X))_\/_{_the_carrier'_of_G}_)_&_(_x_in_(Edges_Out_(v1,X))_\/_{_the_carrier'_of_G}_implies_x_in_Edges_Out_(v9,X)_)_)
let x be set ; ::_thesis: ( ( x in Edges_Out (v9,X) implies x in (Edges_Out (v1,X)) \/ { the carrier' of G} ) & ( x in (Edges_Out (v1,X)) \/ { the carrier' of G} implies b1 in Edges_Out (v9,X) ) )
hereby  ::_thesis: ( x in (Edges_Out (v1,X)) \/ { the carrier' of G} implies b1 in Edges_Out (v9,X) )
assume A4: x in Edges_Out (v9,X) ; ::_thesis: x in (Edges_Out (v1,X)) \/ { the carrier' of G}
then A5: x in X by Def2;
A6: the Source of (AddNewEdge (v1,v2)) . x = v9 by A4, Def2;
percases ( x in the carrier' of G or x in { the carrier' of G} ) by A3, A4, XBOOLE_0:def_3;
supposeA7: x in the carrier' of G ; ::_thesis: x in (Edges_Out (v1,X)) \/ { the carrier' of G}
then  the Source of G . x = v1 by A1, A6, Th35;
then  x in Edges_Out (v1,X) by A5, A7, Def2;
hence  x in (Edges_Out (v1,X)) \/ { the carrier' of G} by XBOOLE_0:def_3; ::_thesis: verum
end;
suppose x in { the carrier' of G} ; ::_thesis: x in (Edges_Out (v1,X)) \/ { the carrier' of G}
hence  x in (Edges_Out (v1,X)) \/ { the carrier' of G} by XBOOLE_0:def_3; ::_thesis: verum
end;
end;
end;
assume A8: x in (Edges_Out (v1,X)) \/ { the carrier' of G} ; ::_thesis: b1 in Edges_Out (v9,X)
percases ( x in Edges_Out (v1,X) or x in { the carrier' of G} ) by A8, XBOOLE_0:def_3;
supposeA9: x in Edges_Out (v1,X) ; ::_thesis: b1 in Edges_Out (v9,X)
then  the Source of G . x = v1 by Def2;
then A10: the Source of (AddNewEdge (v1,v2)) . x = v9 by A1, A9, Th35;
 ( x in X & x in the carrier' of (AddNewEdge (v1,v2)) ) by A3, A9, Def2, XBOOLE_0:def_3;
hence  x in Edges_Out (v9,X) by A10, Def2; ::_thesis: verum
end;
supposeA11: x in { the carrier' of G} ; ::_thesis: b1 in Edges_Out (v9,X)
A12: the Source of (AddNewEdge (v1,v2)) . the carrier' of G = v1 by Th34;
 ( x = the carrier' of G & x in the carrier' of (AddNewEdge (v1,v2)) ) by A3, A11, TARSKI:def_1, XBOOLE_0:def_3;
hence  x in Edges_Out (v9,X) by A1, A2, A12, Def2; ::_thesis: verum
end;
end;
end;
hence  Edges_Out (v9,X) = (Edges_Out (v1,X)) \/ { the carrier' of G} by TARSKI:1; ::_thesis: Edges_Out (v1,X) misses { the carrier' of G}
assume  (Edges_Out (v1,X)) /\ { the carrier' of G} <> {} ; :: according to XBOOLE_0:def_7 ::_thesis: contradiction
then consider x being set  such that
A13: x in (Edges_Out (v1,X)) /\ { the carrier' of G} by XBOOLE_0:def_1;
 x in { the carrier' of G} by A13, XBOOLE_0:def_4;
then A14: x = the carrier' of G by TARSKI:def_1;
 x in the carrier' of G by A13;
hence  contradiction by A14; ::_thesis: verum
end;

theorem Th42: :: GRAPH_3:42
for X being set
for G being Graph
for v1, v2 being Vertex of G
for v9 being Vertex of (AddNewEdge (v1,v2)) st v9 = v2 & the carrier' of G in X holds
( Edges_In (v9,X) = (Edges_In (v2,X)) \/ { the carrier' of G} & Edges_In (v2,X) misses { the carrier' of G} )
proof
let X be set ; ::_thesis: for G being Graph
for v1, v2 being Vertex of G
for v9 being Vertex of (AddNewEdge (v1,v2)) st v9 = v2 & the carrier' of G in X holds
( Edges_In (v9,X) = (Edges_In (v2,X)) \/ { the carrier' of G} & Edges_In (v2,X) misses { the carrier' of G} )
let G be Graph; ::_thesis: for v1, v2 being Vertex of G
for v9 being Vertex of (AddNewEdge (v1,v2)) st v9 = v2 & the carrier' of G in X holds
( Edges_In (v9,X) = (Edges_In (v2,X)) \/ { the carrier' of G} & Edges_In (v2,X) misses { the carrier' of G} )
let v1, v2 be Vertex of G; ::_thesis: for v9 being Vertex of (AddNewEdge (v1,v2)) st v9 = v2 & the carrier' of G in X holds
( Edges_In (v9,X) = (Edges_In (v2,X)) \/ { the carrier' of G} & Edges_In (v2,X) misses { the carrier' of G} )
let v9 be Vertex of (AddNewEdge (v1,v2)); ::_thesis: ( v9 = v2 & the carrier' of G in X implies ( Edges_In (v9,X) = (Edges_In (v2,X)) \/ { the carrier' of G} & Edges_In (v2,X) misses { the carrier' of G} ) )
assume that
A1: v9 = v2 and
A2: the carrier' of G in X ; ::_thesis: ( Edges_In (v9,X) = (Edges_In (v2,X)) \/ { the carrier' of G} & Edges_In (v2,X) misses { the carrier' of G} )
set G9 = AddNewEdge (v1,v2);
set E = the carrier' of G;
set T = the Target of G;
set E9 = the carrier' of (AddNewEdge (v1,v2));
set T9 = the Target of (AddNewEdge (v1,v2));
A3: the carrier' of (AddNewEdge (v1,v2)) = the carrier' of G \/ { the carrier' of G} by Def7;
now__::_thesis:_for_x_being_set_holds_
(_(_x_in_Edges_In_(v9,X)_implies_x_in_(Edges_In_(v2,X))_\/_{_the_carrier'_of_G}_)_&_(_x_in_(Edges_In_(v2,X))_\/_{_the_carrier'_of_G}_implies_x_in_Edges_In_(v9,X)_)_)
let x be set ; ::_thesis: ( ( x in Edges_In (v9,X) implies x in (Edges_In (v2,X)) \/ { the carrier' of G} ) & ( x in (Edges_In (v2,X)) \/ { the carrier' of G} implies b1 in Edges_In (v9,X) ) )
hereby  ::_thesis: ( x in (Edges_In (v2,X)) \/ { the carrier' of G} implies b1 in Edges_In (v9,X) )
assume A4: x in Edges_In (v9,X) ; ::_thesis: x in (Edges_In (v2,X)) \/ { the carrier' of G}
then A5: x in X by Def1;
A6: the Target of (AddNewEdge (v1,v2)) . x = v9 by A4, Def1;
percases ( x in the carrier' of G or x in { the carrier' of G} ) by A3, A4, XBOOLE_0:def_3;
supposeA7: x in the carrier' of G ; ::_thesis: x in (Edges_In (v2,X)) \/ { the carrier' of G}
then  the Target of G . x = v2 by A1, A6, Th35;
then  x in Edges_In (v2,X) by A5, A7, Def1;
hence  x in (Edges_In (v2,X)) \/ { the carrier' of G} by XBOOLE_0:def_3; ::_thesis: verum
end;
suppose x in { the carrier' of G} ; ::_thesis: x in (Edges_In (v2,X)) \/ { the carrier' of G}
hence  x in (Edges_In (v2,X)) \/ { the carrier' of G} by XBOOLE_0:def_3; ::_thesis: verum
end;
end;
end;
assume A8: x in (Edges_In (v2,X)) \/ { the carrier' of G} ; ::_thesis: b1 in Edges_In (v9,X)
percases ( x in Edges_In (v2,X) or x in { the carrier' of G} ) by A8, XBOOLE_0:def_3;
supposeA9: x in Edges_In (v2,X) ; ::_thesis: b1 in Edges_In (v9,X)
then  the Target of G . x = v2 by Def1;
then A10: the Target of (AddNewEdge (v1,v2)) . x = v9 by A1, A9, Th35;
 ( x in X & x in the carrier' of (AddNewEdge (v1,v2)) ) by A3, A9, Def1, XBOOLE_0:def_3;
hence  x in Edges_In (v9,X) by A10, Def1; ::_thesis: verum
end;
supposeA11: x in { the carrier' of G} ; ::_thesis: b1 in Edges_In (v9,X)
A12: the Target of (AddNewEdge (v1,v2)) . the carrier' of G = v2 by Th34;
 ( x = the carrier' of G & x in the carrier' of (AddNewEdge (v1,v2)) ) by A3, A11, TARSKI:def_1, XBOOLE_0:def_3;
hence  x in Edges_In (v9,X) by A1, A2, A12, Def1; ::_thesis: verum
end;
end;
end;
hence  Edges_In (v9,X) = (Edges_In (v2,X)) \/ { the carrier' of G} by TARSKI:1; ::_thesis: Edges_In (v2,X) misses { the carrier' of G}
assume  (Edges_In (v2,X)) /\ { the carrier' of G} <> {} ; :: according to XBOOLE_0:def_7 ::_thesis: contradiction
then consider x being set  such that
A13: x in (Edges_In (v2,X)) /\ { the carrier' of G} by XBOOLE_0:def_1;
 x in { the carrier' of G} by A13, XBOOLE_0:def_4;
then A14: x = the carrier' of G by TARSKI:def_1;
 x in the carrier' of G by A13;
hence  contradiction by A14; ::_thesis: verum
end;

theorem Th43: :: GRAPH_3:43
for X being set
for G being Graph
for v1, v, v2 being Vertex of G
for v9 being Vertex of (AddNewEdge (v1,v2)) st v9 = v & v <> v2 holds
Edges_In (v9,X) = Edges_In (v,X)
proof
let X be set ; ::_thesis: for G being Graph
for v1, v, v2 being Vertex of G
for v9 being Vertex of (AddNewEdge (v1,v2)) st v9 = v & v <> v2 holds
Edges_In (v9,X) = Edges_In (v,X)
let G be Graph; ::_thesis: for v1, v, v2 being Vertex of G
for v9 being Vertex of (AddNewEdge (v1,v2)) st v9 = v & v <> v2 holds
Edges_In (v9,X) = Edges_In (v,X)
let v1, v, v2 be Vertex of G; ::_thesis: for v9 being Vertex of (AddNewEdge (v1,v2)) st v9 = v & v <> v2 holds
Edges_In (v9,X) = Edges_In (v,X)
let v9 be Vertex of (AddNewEdge (v1,v2)); ::_thesis: ( v9 = v & v <> v2 implies Edges_In (v9,X) = Edges_In (v,X) )
assume that
A1: v9 = v and
A2: v <> v2 ; ::_thesis: Edges_In (v9,X) = Edges_In (v,X)
set G9 = AddNewEdge (v1,v2);
set E = the carrier' of G;
set T = the Target of G;
set E9 = the carrier' of (AddNewEdge (v1,v2));
set T9 = the Target of (AddNewEdge (v1,v2));
A3: the carrier' of (AddNewEdge (v1,v2)) = the carrier' of G \/ { the carrier' of G} by Def7;
now__::_thesis:_for_x_being_set_holds_
(_(_x_in_Edges_In_(v9,X)_implies_x_in_Edges_In_(v,X)_)_&_(_x_in_Edges_In_(v,X)_implies_x_in_Edges_In_(v9,X)_)_)
let x be set ; ::_thesis: ( ( x in Edges_In (v9,X) implies x in Edges_In (v,X) ) & ( x in Edges_In (v,X) implies x in Edges_In (v9,X) ) )
hereby  ::_thesis: ( x in Edges_In (v,X) implies x in Edges_In (v9,X) )
assume A4: x in Edges_In (v9,X) ; ::_thesis: x in Edges_In (v,X)
then A5: x in X by Def1;
A6: the Target of (AddNewEdge (v1,v2)) . x = v9 by A4, Def1;
 the Target of (AddNewEdge (v1,v2)) . the carrier' of G = v2 by Th34;
then  not x in { the carrier' of G} by A1, A2, A6, TARSKI:def_1;
then A7: x in the carrier' of G by A3, A4, XBOOLE_0:def_3;
then  the Target of G . x = v by A1, A6, Th35;
hence  x in Edges_In (v,X) by A5, A7, Def1; ::_thesis: verum
end;
assume A8: x in Edges_In (v,X) ; ::_thesis: x in Edges_In (v9,X)
then  the Target of G . x = v by Def1;
then A9: the Target of (AddNewEdge (v1,v2)) . x = v9 by A1, A8, Th35;
 ( x in X & x in the carrier' of (AddNewEdge (v1,v2)) ) by A3, A8, Def1, XBOOLE_0:def_3;
hence  x in Edges_In (v9,X) by A9, Def1; ::_thesis: verum
end;
hence  Edges_In (v9,X) = Edges_In (v,X) by TARSKI:1; ::_thesis: verum
end;

theorem Th44: :: GRAPH_3:44
for X being set
for G being Graph
for v2, v, v1 being Vertex of G
for v9 being Vertex of (AddNewEdge (v1,v2)) st v9 = v & v <> v1 holds
Edges_Out (v9,X) = Edges_Out (v,X)
proof
let X be set ; ::_thesis: for G being Graph
for v2, v, v1 being Vertex of G
for v9 being Vertex of (AddNewEdge (v1,v2)) st v9 = v & v <> v1 holds
Edges_Out (v9,X) = Edges_Out (v,X)
let G be Graph; ::_thesis: for v2, v, v1 being Vertex of G
for v9 being Vertex of (AddNewEdge (v1,v2)) st v9 = v & v <> v1 holds
Edges_Out (v9,X) = Edges_Out (v,X)
let v2, v, v1 be Vertex of G; ::_thesis: for v9 being Vertex of (AddNewEdge (v1,v2)) st v9 = v & v <> v1 holds
Edges_Out (v9,X) = Edges_Out (v,X)
let v9 be Vertex of (AddNewEdge (v1,v2)); ::_thesis: ( v9 = v & v <> v1 implies Edges_Out (v9,X) = Edges_Out (v,X) )
assume that
A1: v9 = v and
A2: v <> v1 ; ::_thesis: Edges_Out (v9,X) = Edges_Out (v,X)
set G9 = AddNewEdge (v1,v2);
set E = the carrier' of G;
set S = the Source of G;
set E9 = the carrier' of (AddNewEdge (v1,v2));
set S9 = the Source of (AddNewEdge (v1,v2));
A3: the carrier' of (AddNewEdge (v1,v2)) = the carrier' of G \/ { the carrier' of G} by Def7;
now__::_thesis:_for_x_being_set_holds_
(_(_x_in_Edges_Out_(v9,X)_implies_x_in_Edges_Out_(v,X)_)_&_(_x_in_Edges_Out_(v,X)_implies_x_in_Edges_Out_(v9,X)_)_)
let x be set ; ::_thesis: ( ( x in Edges_Out (v9,X) implies x in Edges_Out (v,X) ) & ( x in Edges_Out (v,X) implies x in Edges_Out (v9,X) ) )
hereby  ::_thesis: ( x in Edges_Out (v,X) implies x in Edges_Out (v9,X) )
assume A4: x in Edges_Out (v9,X) ; ::_thesis: x in Edges_Out (v,X)
then A5: x in X by Def2;
A6: the Source of (AddNewEdge (v1,v2)) . x = v9 by A4, Def2;
 the Source of (AddNewEdge (v1,v2)) . the carrier' of G = v1 by Th34;
then  not x in { the carrier' of G} by A1, A2, A6, TARSKI:def_1;
then A7: x in the carrier' of G by A3, A4, XBOOLE_0:def_3;
then  the Source of G . x = v by A1, A6, Th35;
hence  x in Edges_Out (v,X) by A5, A7, Def2; ::_thesis: verum
end;
assume A8: x in Edges_Out (v,X) ; ::_thesis: x in Edges_Out (v9,X)
then  the Source of G . x = v by Def2;
then A9: the Source of (AddNewEdge (v1,v2)) . x = v9 by A1, A8, Th35;
 ( x in X & x in the carrier' of (AddNewEdge (v1,v2)) ) by A3, A8, Def2, XBOOLE_0:def_3;
hence  x in Edges_Out (v9,X) by A9, Def2; ::_thesis: verum
end;
hence  Edges_Out (v9,X) = Edges_Out (v,X) by TARSKI:1; ::_thesis: verum
end;

theorem Th45: :: GRAPH_3:45
for G being Graph
for v1, v2 being Vertex of G
for p9 being Path of AddNewEdge (v1,v2) st not the carrier' of G in rng p9 holds
p9 is Path of G
proof
let G be Graph; ::_thesis: for v1, v2 being Vertex of G
for p9 being Path of AddNewEdge (v1,v2) st not the carrier' of G in rng p9 holds
p9 is Path of G
let v1, v2 be Vertex of G; ::_thesis: for p9 being Path of AddNewEdge (v1,v2) st not the carrier' of G in rng p9 holds
p9 is Path of G
let p9 be Path of AddNewEdge (v1,v2); ::_thesis: ( not the carrier' of G in rng p9 implies p9 is Path of G )
set G9 = AddNewEdge (v1,v2);
set S = the Source of G;
set T = the Target of G;
set E = the carrier' of G;
set S9 = the Source of (AddNewEdge (v1,v2));
set T9 = the Target of (AddNewEdge (v1,v2));
 the carrier' of (AddNewEdge (v1,v2)) = the carrier' of G \/ { the carrier' of G} by Def7;
then A1: rng p9 c= the carrier' of G \/ { the carrier' of G} by FINSEQ_1:def_4;
assume A2: not the carrier' of G in rng p9 ; ::_thesis: p9 is Path of G
A3: rng p9 c= the carrier' of G
proof
let x be set ; :: according to TARSKI:def_3 ::_thesis: ( not x in rng p9 or x in the carrier' of G )
assume A4: x in rng p9 ; ::_thesis: x in the carrier' of G
then  ( x in the carrier' of G or x in { the carrier' of G} ) by A1, XBOOLE_0:def_3;
hence  x in the carrier' of G by A2, A4, TARSKI:def_1; ::_thesis: verum
end;
 p9 is Chain of G
proof
thus  p9 is FinSequence of the carrier' of G by A3, FINSEQ_1:def_4; :: according to MSSCYC_1:def_1 ::_thesis: ex b1 being FinSequence of the carrier of G st b1 is_vertex_seq_of p9
consider vs9 being FinSequence of the carrier of (AddNewEdge (v1,v2)) such that
A5: vs9 is_vertex_seq_of p9 by MSSCYC_1:def_1;
reconsider vs = vs9 as FinSequence of the carrier of G by Def7;
take  vs ; ::_thesis: vs is_vertex_seq_of p9
thus  vs is_vertex_seq_of p9 ::_thesis: verum
proof
thus A6: len vs = (len p9) + 1 by A5, GRAPH_2:def_6; :: according to GRAPH_2:def_6 ::_thesis: for b1 being Element of NAT holds
( not 1 <= b1 or not b1 <= len p9 or p9 . b1 joins vs /. b1,vs /. (b1 + 1) )
let n be Element of NAT ; ::_thesis: ( not 1 <= n or not n <= len p9 or p9 . n joins vs /. n,vs /. (n + 1) )
assume that
A7: 1 <= n and
A8: n <= len p9 ; ::_thesis: p9 . n joins vs /. n,vs /. (n + 1)
set e = p9 . n;
reconsider vn9 = vs9 /. n, vn19 = vs9 /. (n + 1) as Vertex of (AddNewEdge (v1,v2)) ;
 p9 . n joins vs9 /. n,vs9 /. (n + 1) by A5, A7, A8, GRAPH_2:def_6;
then A9: ( ( the Source of (AddNewEdge (v1,v2)) . (p9 . n) = vn9 & the Target of (AddNewEdge (v1,v2)) . (p9 . n) = vn19 ) or ( the Source of (AddNewEdge (v1,v2)) . (p9 . n) = vn19 & the Target of (AddNewEdge (v1,v2)) . (p9 . n) = vn9 ) ) by GRAPH_1:def_12;
reconsider vn = vs /. n, vn1 = vs /. (n + 1) as Vertex of G ;
 ( 1 <= n + 1 & n + 1 <= len vs ) by A6, A8, NAT_1:11, XREAL_1:6;
then A10: n + 1 in dom vs by FINSEQ_3:25;
then A11: vn1 = vs . (n + 1) by PARTFUN1:def_6
.= vn19 by A10, PARTFUN1:def_6 ;
 n in dom p9 by A7, A8, FINSEQ_3:25;
then  p9 . n in rng p9 by FUNCT_1:def_3;
then A12: ( the Source of (AddNewEdge (v1,v2)) . (p9 . n) = the Source of G . (p9 . n) & the Target of (AddNewEdge (v1,v2)) . (p9 . n) = the Target of G . (p9 . n) ) by A3, Th35;
 len p9 <= len vs by A6, NAT_1:11;
then  n <= len vs by A8, XXREAL_0:2;
then A13: n in dom vs by A7, FINSEQ_3:25;
then vn = vs . n by PARTFUN1:def_6
.= vn9 by A13, PARTFUN1:def_6 ;
hence  p9 . n joins vs /. n,vs /. (n + 1) by A9, A12, A11, GRAPH_1:def_12; ::_thesis: verum
end;
end;
then reconsider p99 = p9 as Chain of G ;
 p99 is V14() ;
hence  p9 is Path of G ; ::_thesis: verum
end;

theorem Th46: :: GRAPH_3:46
for G being Graph
for v1, v2 being Vertex of G
for vs being FinSequence of the carrier of G
for p9 being Path of AddNewEdge (v1,v2)
for vs9 being FinSequence of the carrier of (AddNewEdge (v1,v2)) st not the carrier' of G in rng p9 & vs = vs9 & vs9 is_vertex_seq_of p9 holds
vs is_vertex_seq_of p9
proof
let G be Graph; ::_thesis: for v1, v2 being Vertex of G
for vs being FinSequence of the carrier of G
for p9 being Path of AddNewEdge (v1,v2)
for vs9 being FinSequence of the carrier of (AddNewEdge (v1,v2)) st not the carrier' of G in rng p9 & vs = vs9 & vs9 is_vertex_seq_of p9 holds
vs is_vertex_seq_of p9
let v1, v2 be Vertex of G; ::_thesis: for vs being FinSequence of the carrier of G
for p9 being Path of AddNewEdge (v1,v2)
for vs9 being FinSequence of the carrier of (AddNewEdge (v1,v2)) st not the carrier' of G in rng p9 & vs = vs9 & vs9 is_vertex_seq_of p9 holds
vs is_vertex_seq_of p9
let vs be FinSequence of the carrier of G; ::_thesis: for p9 being Path of AddNewEdge (v1,v2)
for vs9 being FinSequence of the carrier of (AddNewEdge (v1,v2)) st not the carrier' of G in rng p9 & vs = vs9 & vs9 is_vertex_seq_of p9 holds
vs is_vertex_seq_of p9
let p9 be Path of AddNewEdge (v1,v2); ::_thesis: for vs9 being FinSequence of the carrier of (AddNewEdge (v1,v2)) st not the carrier' of G in rng p9 & vs = vs9 & vs9 is_vertex_seq_of p9 holds
vs is_vertex_seq_of p9
let vs9 be FinSequence of the carrier of (AddNewEdge (v1,v2)); ::_thesis: ( not the carrier' of G in rng p9 & vs = vs9 & vs9 is_vertex_seq_of p9 implies vs is_vertex_seq_of p9 )
set G9 = AddNewEdge (v1,v2);
set S = the Source of G;
set T = the Target of G;
set E = the carrier' of G;
set S9 = the Source of (AddNewEdge (v1,v2));
set T9 = the Target of (AddNewEdge (v1,v2));
 the carrier' of (AddNewEdge (v1,v2)) = the carrier' of G \/ { the carrier' of G} by Def7;
then A1: rng p9 c= the carrier' of G \/ { the carrier' of G} by FINSEQ_1:def_4;
assume A2: not the carrier' of G in rng p9 ; ::_thesis: ( not vs = vs9 or not vs9 is_vertex_seq_of p9 or vs is_vertex_seq_of p9 )
A3: rng p9 c= the carrier' of G
proof
let x be set ; :: according to TARSKI:def_3 ::_thesis: ( not x in rng p9 or x in the carrier' of G )
assume A4: x in rng p9 ; ::_thesis: x in the carrier' of G
then  ( x in the carrier' of G or x in { the carrier' of G} ) by A1, XBOOLE_0:def_3;
hence  x in the carrier' of G by A2, A4, TARSKI:def_1; ::_thesis: verum
end;
assume that
A5: vs = vs9 and
A6: vs9 is_vertex_seq_of p9 ; ::_thesis: vs is_vertex_seq_of p9
thus  vs is_vertex_seq_of p9 ::_thesis: verum
proof
thus A7: len vs = (len p9) + 1 by A5, A6, GRAPH_2:def_6; :: according to GRAPH_2:def_6 ::_thesis: for b1 being Element of NAT holds
( not 1 <= b1 or not b1 <= len p9 or p9 . b1 joins vs /. b1,vs /. (b1 + 1) )
let n be Element of NAT ; ::_thesis: ( not 1 <= n or not n <= len p9 or p9 . n joins vs /. n,vs /. (n + 1) )
assume that
A8: 1 <= n and
A9: n <= len p9 ; ::_thesis: p9 . n joins vs /. n,vs /. (n + 1)
set e = p9 . n;
reconsider vn9 = vs9 /. n, vn19 = vs9 /. (n + 1) as Vertex of (AddNewEdge (v1,v2)) ;
 p9 . n joins vs9 /. n,vs9 /. (n + 1) by A6, A8, A9, GRAPH_2:def_6;
then A10: ( ( the Source of (AddNewEdge (v1,v2)) . (p9 . n) = vn9 & the Target of (AddNewEdge (v1,v2)) . (p9 . n) = vn19 ) or ( the Source of (AddNewEdge (v1,v2)) . (p9 . n) = vn19 & the Target of (AddNewEdge (v1,v2)) . (p9 . n) = vn9 ) ) by GRAPH_1:def_12;
reconsider vn = vs /. n, vn1 = vs /. (n + 1) as Vertex of G ;
 ( 1 <= n + 1 & n + 1 <= len vs ) by A7, A9, NAT_1:11, XREAL_1:6;
then A11: n + 1 in dom vs by FINSEQ_3:25;
then A12: vn1 = vs . (n + 1) by PARTFUN1:def_6
.= vn19 by A5, A11, PARTFUN1:def_6 ;
 n in dom p9 by A8, A9, FINSEQ_3:25;
then  p9 . n in rng p9 by FUNCT_1:def_3;
then A13: ( the Source of (AddNewEdge (v1,v2)) . (p9 . n) = the Source of G . (p9 . n) & the Target of (AddNewEdge (v1,v2)) . (p9 . n) = the Target of G . (p9 . n) ) by A3, Th35;
 len p9 <= len vs by A7, NAT_1:11;
then  n <= len vs by A9, XXREAL_0:2;
then A14: n in dom vs by A8, FINSEQ_3:25;
then vn = vs . n by PARTFUN1:def_6
.= vn9 by A5, A14, PARTFUN1:def_6 ;
hence  p9 . n joins vs /. n,vs /. (n + 1) by A10, A13, A12, GRAPH_1:def_12; ::_thesis: verum
end;
end;

registration
let G be connected Graph;
let v1, v2 be Vertex of G;
cluster AddNewEdge (v1,v2) ->  strict connected ;
coherence
 AddNewEdge (v1,v2) is connected
proof
set G9 = AddNewEdge (v1,v2);
now__::_thesis:_for_v19,_v29_being_Vertex_of_(AddNewEdge_(v1,v2))_st_v19_<>_v29_holds_
ex_c9_being_Chain_of_AddNewEdge_(v1,v2)_ex_vs9_being_FinSequence_of_the_carrier_of_(AddNewEdge_(v1,v2))_st_
(_not_c9_is_empty_&_vs9_is_vertex_seq_of_c9_&_vs9_._1_=_v19_&_vs9_._(len_vs9)_=_v29_)
let v19, v29 be Vertex of (AddNewEdge (v1,v2)); ::_thesis: ( v19 <> v29 implies ex c9 being Chain of AddNewEdge (v1,v2) ex vs9 being FinSequence of the carrier of (AddNewEdge (v1,v2)) st
( not c9 is empty & vs9 is_vertex_seq_of c9 & vs9 . 1 = v19 & vs9 . (len vs9) = v29 ) )
reconsider v1 = v19, v2 = v29 as Vertex of G by Def7;
assume  v19 <> v29 ; ::_thesis: ex c9 being Chain of AddNewEdge (v1,v2) ex vs9 being FinSequence of the carrier of (AddNewEdge (v1,v2)) st
( not c9 is empty & vs9 is_vertex_seq_of c9 & vs9 . 1 = v19 & vs9 . (len vs9) = v29 )
then consider c being Chain of G, vs being FinSequence of the carrier of G such that
A1: not c is empty and
A2: vs is_vertex_seq_of c and
A3: ( vs . 1 = v1 & vs . (len vs) = v2 ) by Th18;
reconsider vs9 = vs as FinSequence of the carrier of (AddNewEdge (v1,v2)) by Def7;
reconsider c9 = c as Chain of AddNewEdge (v1,v2) by Th37;
take c9 = c9; ::_thesis: ex vs9 being FinSequence of the carrier of (AddNewEdge (v1,v2)) st
( not c9 is empty & vs9 is_vertex_seq_of c9 & vs9 . 1 = v19 & vs9 . (len vs9) = v29 )
take vs9 = vs9; ::_thesis: ( not c9 is empty & vs9 is_vertex_seq_of c9 & vs9 . 1 = v19 & vs9 . (len vs9) = v29 )
thus  not c9 is empty by A1; ::_thesis: ( vs9 is_vertex_seq_of c9 & vs9 . 1 = v19 & vs9 . (len vs9) = v29 )
thus  vs9 is_vertex_seq_of c9 by A2, Th36; ::_thesis: ( vs9 . 1 = v19 & vs9 . (len vs9) = v29 )
thus  ( vs9 . 1 = v19 & vs9 . (len vs9) = v29 ) by A3; ::_thesis: verum
end;
hence  AddNewEdge (v1,v2) is connected by Th18; ::_thesis: verum
end;
end;


theorem Th47: :: GRAPH_3:47
for X being set
for G being finite Graph
for v, v1, v2 being Vertex of G
for v9 being Vertex of (AddNewEdge (v1,v2)) st v9 = v & v1 <> v2 & ( v = v1 or v = v2 ) & the carrier' of G in X holds
Degree (v9,X) = (Degree (v,X)) + 1
proof
let X be set ; ::_thesis: for G being finite Graph
for v, v1, v2 being Vertex of G
for v9 being Vertex of (AddNewEdge (v1,v2)) st v9 = v & v1 <> v2 & ( v = v1 or v = v2 ) & the carrier' of G in X holds
Degree (v9,X) = (Degree (v,X)) + 1
let G be finite Graph; ::_thesis: for v, v1, v2 being Vertex of G
for v9 being Vertex of (AddNewEdge (v1,v2)) st v9 = v & v1 <> v2 & ( v = v1 or v = v2 ) & the carrier' of G in X holds
Degree (v9,X) = (Degree (v,X)) + 1
let v, v1, v2 be Vertex of G; ::_thesis: for v9 being Vertex of (AddNewEdge (v1,v2)) st v9 = v & v1 <> v2 & ( v = v1 or v = v2 ) & the carrier' of G in X holds
Degree (v9,X) = (Degree (v,X)) + 1
let v9 be Vertex of (AddNewEdge (v1,v2)); ::_thesis: ( v9 = v & v1 <> v2 & ( v = v1 or v = v2 ) & the carrier' of G in X implies Degree (v9,X) = (Degree (v,X)) + 1 )
assume that
A1: v9 = v and
A2: v1 <> v2 and
A3: ( v = v1 or v = v2 ) and
A4: the carrier' of G in X ; ::_thesis: Degree (v9,X) = (Degree (v,X)) + 1
set E = the carrier' of G;
percases ( v = v1 or v = v2 ) by A3;
supposeA5: v = v1 ; ::_thesis: Degree (v9,X) = (Degree (v,X)) + 1
then  ( Edges_In (v9,X) = Edges_In (v,X) & Edges_Out (v9,X) = (Edges_Out (v,X)) \/ { the carrier' of G} ) by A1, A2, A4, Th39, Th41;
hence  Degree (v9,X) = (card (Edges_In (v,X))) + ((card (Edges_Out (v,X))) + (card { the carrier' of G})) by A1, A4, A5, Th41, CARD_2:40
.= ((card (Edges_In (v,X))) + (card (Edges_Out (v,X)))) + (card { the carrier' of G})
.= (Degree (v,X)) + 1 by CARD_1:30 ;
::_thesis: verum
end;
supposeA6: v = v2 ; ::_thesis: Degree (v9,X) = (Degree (v,X)) + 1
then  ( Edges_Out (v9,X) = Edges_Out (v,X) & Edges_In (v9,X) = (Edges_In (v,X)) \/ { the carrier' of G} ) by A1, A2, A4, Th40, Th42;
hence  Degree (v9,X) = ((card (Edges_In (v,X))) + (card { the carrier' of G})) + (card (Edges_Out (v,X))) by A1, A4, A6, Th42, CARD_2:40
.= ((card (Edges_In (v,X))) + (card (Edges_Out (v,X)))) + (card { the carrier' of G})
.= (Degree (v,X)) + 1 by CARD_1:30 ;
::_thesis: verum
end;
end;
end;

theorem Th48: :: GRAPH_3:48
for X being set
for G being finite Graph
for v, v1, v2 being Vertex of G
for v9 being Vertex of (AddNewEdge (v1,v2)) st v9 = v & v <> v1 & v <> v2 holds
Degree (v9,X) = Degree (v,X)
proof
let X be set ; ::_thesis: for G being finite Graph
for v, v1, v2 being Vertex of G
for v9 being Vertex of (AddNewEdge (v1,v2)) st v9 = v & v <> v1 & v <> v2 holds
Degree (v9,X) = Degree (v,X)
let G be finite Graph; ::_thesis: for v, v1, v2 being Vertex of G
for v9 being Vertex of (AddNewEdge (v1,v2)) st v9 = v & v <> v1 & v <> v2 holds
Degree (v9,X) = Degree (v,X)
let v, v1, v2 be Vertex of G; ::_thesis: for v9 being Vertex of (AddNewEdge (v1,v2)) st v9 = v & v <> v1 & v <> v2 holds
Degree (v9,X) = Degree (v,X)
let v9 be Vertex of (AddNewEdge (v1,v2)); ::_thesis: ( v9 = v & v <> v1 & v <> v2 implies Degree (v9,X) = Degree (v,X) )
assume that
A1: v9 = v and
A2: v <> v1 and
A3: v <> v2 ; ::_thesis: Degree (v9,X) = Degree (v,X)
thus  Degree (v9,X) = (card (Edges_In (v,X))) + (card (Edges_Out (v9,X))) by A1, A3, Th43
.= Degree (v,X) by A1, A2, Th44 ; ::_thesis: verum
end;

begin

Lm4:  for G being finite Graph
for c being cyclic Path of G
for vs being FinSequence of the carrier of G
for v being Vertex of G st vs is_vertex_seq_of c & v in rng vs holds
Degree (v,(rng c)) is even
proof
let G be finite Graph; ::_thesis: for c being cyclic Path of G
for vs being FinSequence of the carrier of G
for v being Vertex of G st vs is_vertex_seq_of c & v in rng vs holds
Degree (v,(rng c)) is even
let c be cyclic Path of G; ::_thesis: for vs being FinSequence of the carrier of G
for v being Vertex of G st vs is_vertex_seq_of c & v in rng vs holds
Degree (v,(rng c)) is even
let vs be FinSequence of the carrier of G; ::_thesis: for v being Vertex of G st vs is_vertex_seq_of c & v in rng vs holds
Degree (v,(rng c)) is even
let v be Vertex of G; ::_thesis: ( vs is_vertex_seq_of c & v in rng vs implies Degree (v,(rng c)) is even )
assume that
A1: vs is_vertex_seq_of c and
A2: v in rng vs ; ::_thesis: Degree (v,(rng c)) is even
set S = the Source of G;
set T = the Target of G;
percases ( c is empty or not c is empty ) ;
suppose c is empty ; ::_thesis: Degree (v,(rng c)) is even
then reconsider rc = rng c as empty set ;
 Degree (v,rc) = 2 * 0 ;
hence  Degree (v,(rng c)) is even ; ::_thesis: verum
end;
supposeA3: not c is empty ; ::_thesis: Degree (v,(rng c)) is even
set ev =  {  n where n is Element of NAT : ( 1 <= n & n <= len c & vs . n = v )  }  ;
A4:  {  n where n is Element of NAT : ( 1 <= n & n <= len c & vs . n = v )  }  c= Seg (len c)
proof
let x be set ; :: according to TARSKI:def_3 ::_thesis: ( not x in  {  n where n is Element of NAT : ( 1 <= n & n <= len c & vs . n = v )  }  or x in Seg (len c) )
assume  x in  {  n where n is Element of NAT : ( 1 <= n & n <= len c & vs . n = v )  }  ; ::_thesis: x in Seg (len c)
then  ex n being Element of NAT st
( x = n & 1 <= n & n <= len c & vs . n = v ) ;
hence  x in Seg (len c) by FINSEQ_1:1; ::_thesis: verum
end;
reconsider rc = rng c as non empty set by A3;
A5: len vs = (len c) + 1 by A1, GRAPH_2:def_6;
set evout = [:{1},(Edges_Out (v,rc)):];
set evin = [:{0},(Edges_In (v,rc)):];
A6: card [:{1},(Edges_Out (v,rc)):] = (card {1}) * (card (Edges_Out (v,rc))) by CARD_2:46
.= 1 * (card (Edges_Out (v,rc))) by CARD_1:30
.= card (Edges_Out (v,rc)) ;
A7: card [:{0},(Edges_In (v,rc)):] = (card {0}) * (card (Edges_In (v,rc))) by CARD_2:46
.= 1 * (card (Edges_In (v,rc))) by CARD_1:30
.= card (Edges_In (v,rc)) ;
now__::_thesis:_not_[:{0},(Edges_In_(v,rc)):]_\/_[:{1},(Edges_Out_(v,rc)):]_is_empty
assume A8: [:{0},(Edges_In (v,rc)):] \/ [:{1},(Edges_Out (v,rc)):] is empty ; ::_thesis: contradiction
then  [:{0},(Edges_In (v,rc)):] is empty ;
then  Degree (v,rc) = 0 + 0 by A7, A6, A8;
hence  contradiction by A1, A2, A3, Th32; ::_thesis: verum
end;
then reconsider evio = [:{0},(Edges_In (v,rc)):] \/ [:{1},(Edges_Out (v,rc)):] as non empty set ;
A9: [:{0},(Edges_In (v,rc)):] misses [:{1},(Edges_Out (v,rc)):]
proof
assume  not [:{0},(Edges_In (v,rc)):] misses [:{1},(Edges_Out (v,rc)):] ; ::_thesis: contradiction
then consider x being set  such that
A10: x in [:{0},(Edges_In (v,rc)):] /\ [:{1},(Edges_Out (v,rc)):] by XBOOLE_0:4;
 x in [:{1},(Edges_Out (v,rc)):] by A10, XBOOLE_0:def_4;
then consider x21, x22 being set  such that
A11: x21 in {1} and
 x22 in Edges_Out (v,rc) and
A12: x = [x21,x22] by ZFMISC_1:def_2;
A13: x21 = 1 by A11, TARSKI:def_1;
 x in [:{0},(Edges_In (v,rc)):] by A10, XBOOLE_0:def_4;
then consider x11, x12 being set  such that
A14: x11 in {0} and
 x12 in Edges_In (v,rc) and
A15: x = [x11,x12] by ZFMISC_1:def_2;
 x11 = 0 by A14, TARSKI:def_1;
hence  contradiction by A15, A12, A13, XTUPLE_0:1; ::_thesis: verum
end;
reconsider ev =  {  n where n is Element of NAT : ( 1 <= n & n <= len c & vs . n = v )  }  as Subset of (Seg (len c)) by A4;
A16: rc c= the carrier' of G by FINSEQ_1:def_4;
then reconsider G9 = G as non void finite Graph ;
reconsider vs9 = vs as FinSequence of the carrier of G9 ;
A17: vs9 . 1 = vs . (len vs) by A1, MSSCYC_1:6;
now__::_thesis:_not_ev_is_empty
A18: 0 + 1 <= len c by A3, NAT_1:13;
consider n being set  such that
A19: n in dom vs and
A20: vs . n = v by A2, FUNCT_1:def_3;
reconsider n = n as Element of NAT by A19;
A21: n <= len vs by A19, FINSEQ_3:25;
A22: 1 <= n by A19, FINSEQ_3:25;
thus  not ev is empty ::_thesis: verum
proof
percases ( n = len vs or n < len vs ) by A21, XXREAL_0:1;
suppose n = len vs ; ::_thesis: not ev is empty
then  1 in ev by A17, A20, A18;
hence  not ev is empty ; ::_thesis: verum
end;
suppose n < len vs ; ::_thesis: not ev is empty
then  n <= len c by A5, NAT_1:13;
then  n in ev by A20, A22;
hence  not ev is empty ; ::_thesis: verum
end;
end;
end;
end;
then reconsider ev = ev as non empty finite set ;
set ev92 = [:2,ev:];
now__::_thesis:_ex_Z_being_set_st_
(_(_for_x_being_set_st_x_in_[:2,ev:]_holds_
ex_y_being_set_st_
(_y_in_[:{0},(Edges_In_(v,rc)):]_\/_[:{1},(Edges_Out_(v,rc)):]_&_[x,y]_in_Z_)_)_&_(_for_y_being_set_st_y_in_[:{0},(Edges_In_(v,rc)):]_\/_[:{1},(Edges_Out_(v,rc)):]_holds_
ex_x_being_set_st_
(_x_in_[:2,ev:]_&_[x,y]_in_Z_)_)_&_(_for_x,_y,_z,_u_being_set_st_[x,y]_in_Z_&_[z,u]_in_Z_holds_
(_x_=_z_iff_y_=_u_)_)_)
defpred S1[ Element of [:2,ev:], Element of evio, Element of NAT ] means ( $1 = [1,$3] & ( ( vs . $3 = the Source of G . (c . $3) & $2 = [1,(c . $3)] ) or ( vs . $3 = the Target of G . (c . $3) & $2 = [0,(c . $3)] & the Target of G . (c . $3) <> the Source of G . (c . $3) ) ) );
defpred S2[ Element of [:2,ev:], Element of evio, Element of NAT ] means ( $1 = [0,$3] & ( ex k being Element of NAT st
( 1 <= k & $3 = k + 1 & ( ( vs . $3 = the Target of G . (c . k) & $2 = [0,(c . k)] ) or ( vs . $3 = the Source of G . (c . k) & $2 = [1,(c . k)] & the Target of G . (c . k) <> the Source of G . (c . k) ) ) ) or ( $3 = 1 & ( ( vs . 1 = the Target of G . (c . (len c)) & $2 = [0,(c . (len c))] ) or ( vs . 1 = the Source of G . (c . (len c)) & $2 = [1,(c . (len c))] & the Target of G . (c . (len c)) <> the Source of G . (c . (len c)) ) ) ) ) );
take Z =  {  [x,y] where x is Element of [:2,ev:], y is Element of evio : ex n being Element of NAT st
( 1 <= n & n <= len c & ( S2[x,y,n] or S1[x,y,n] ) )  }  ; ::_thesis: ( ( for x being set st x in [:2,ev:] holds
ex y being set st
( y in [:{0},(Edges_In (v,rc)):] \/ [:{1},(Edges_Out (v,rc)):] & [x,y] in Z ) ) & ( for y being set st y in [:{0},(Edges_In (v,rc)):] \/ [:{1},(Edges_Out (v,rc)):] holds
ex x being set st
( x in [:2,ev:] & [x,y] in Z ) ) & ( for x, y, z, u being set st [x,y] in Z & [z,u] in Z holds
( x = z iff y = u ) ) )
thus  for x being set st x in [:2,ev:] holds
ex y being set st
( y in [:{0},(Edges_In (v,rc)):] \/ [:{1},(Edges_Out (v,rc)):] & [x,y] in Z ) ::_thesis: ( ( for y being set st y in [:{0},(Edges_In (v,rc)):] \/ [:{1},(Edges_Out (v,rc)):] holds
ex x being set st
( x in [:2,ev:] & [x,y] in Z ) ) & ( for x, y, z, u being set st [x,y] in Z & [z,u] in Z holds
( x = z iff y = u ) ) )
proof
A23: 1 in {1} by TARSKI:def_1;
let x be set ; ::_thesis: ( x in [:2,ev:] implies ex y being set st
( y in [:{0},(Edges_In (v,rc)):] \/ [:{1},(Edges_Out (v,rc)):] & [x,y] in Z ) )
A24: 0 in {0} by TARSKI:def_1;
assume A25: x in [:2,ev:] ; ::_thesis: ex y being set st
( y in [:{0},(Edges_In (v,rc)):] \/ [:{1},(Edges_Out (v,rc)):] & [x,y] in Z )
then consider u, w being set  such that
A26: [u,w] = x by RELAT_1:def_1;
reconsider x9 = x as Element of [:2,ev:] by A25;
A27: u in 2 by A25, A26, ZFMISC_1:87;
 w in ev by A25, A26, ZFMISC_1:87;
then consider n being Element of NAT  such that
A28: w = n and
A29: 1 <= n and
A30: n <= len c and
A31: vs . n = v ;
percases ( u = 0 or u = 1 ) by A27, CARD_1:50, TARSKI:def_2;
supposeA32: u = 0 ; ::_thesis: ex y being set st
( y in [:{0},(Edges_In (v,rc)):] \/ [:{1},(Edges_Out (v,rc)):] & [x,y] in Z )
thus  ex y being set st
( y in [:{0},(Edges_In (v,rc)):] \/ [:{1},(Edges_Out (v,rc)):] & [x,y] in Z ) ::_thesis: verum
proof
percases ( 1 < n or n = 1 ) by A29, XXREAL_0:1;
suppose 1 < n ; ::_thesis: ex y being set st
( y in [:{0},(Edges_In (v,rc)):] \/ [:{1},(Edges_Out (v,rc)):] & [x,y] in Z )
then consider k being Element of NAT  such that
A33: n = 1 + k and
A34: 1 <= k by FINSEQ_4:84;
 k <= n by A33, NAT_1:11;
then A35: k <= len c by A30, XXREAL_0:2;
then  k in dom c by A34, FINSEQ_3:25;
then reconsider e = c . k as Element of rc by FUNCT_1:def_3;
A36: e in rc ;
thus  ex y being set st
( y in [:{0},(Edges_In (v,rc)):] \/ [:{1},(Edges_Out (v,rc)):] & [x,y] in Z ) ::_thesis: verum
proof
percases ( the Target of G . (c . k) = vs . (k + 1) or ( the Source of G . (c . k) = vs . (k + 1) & the Target of G . (c . k) <> the Source of G . (c . k) ) ) by A1, A34, A35, Lm3;
supposeA37: the Target of G . (c . k) = vs . (k + 1) ; ::_thesis: ex y being set st
( y in [:{0},(Edges_In (v,rc)):] \/ [:{1},(Edges_Out (v,rc)):] & [x,y] in Z )
take y = [0,(c . k)]; ::_thesis: ( y in [:{0},(Edges_In (v,rc)):] \/ [:{1},(Edges_Out (v,rc)):] & [x,y] in Z )
 e in Edges_In (v,rc) by A16, A31, A33, A36, A37, Def1;
then A38: y in [:{0},(Edges_In (v,rc)):] by A24, ZFMISC_1:87;
hence  y in [:{0},(Edges_In (v,rc)):] \/ [:{1},(Edges_Out (v,rc)):] by XBOOLE_0:def_3; ::_thesis: [x,y] in Z
reconsider y9 = y as Element of evio by A38, XBOOLE_0:def_3;
 S2[x9,y9,n] by A26, A28, A32, A33, A34, A37;
hence  [x,y] in Z by A29, A30; ::_thesis: verum
end;
supposeA39: ( the Source of G . (c . k) = vs . (k + 1) & the Target of G . (c . k) <> the Source of G . (c . k) ) ; ::_thesis: ex y being set st
( y in [:{0},(Edges_In (v,rc)):] \/ [:{1},(Edges_Out (v,rc)):] & [x,y] in Z )
take y = [1,(c . k)]; ::_thesis: ( y in [:{0},(Edges_In (v,rc)):] \/ [:{1},(Edges_Out (v,rc)):] & [x,y] in Z )
 e in Edges_Out (v,rc) by A16, A31, A33, A36, A39, Def2;
then A40: y in [:{1},(Edges_Out (v,rc)):] by A23, ZFMISC_1:87;
hence  y in [:{0},(Edges_In (v,rc)):] \/ [:{1},(Edges_Out (v,rc)):] by XBOOLE_0:def_3; ::_thesis: [x,y] in Z
reconsider y9 = y as Element of evio by A40, XBOOLE_0:def_3;
 S2[x9,y9,n] by A26, A28, A32, A33, A34, A39;
hence  [x,y] in Z by A29, A30; ::_thesis: verum
end;
end;
end;
end;
supposeA41: n = 1 ; ::_thesis: ex y being set st
( y in [:{0},(Edges_In (v,rc)):] \/ [:{1},(Edges_Out (v,rc)):] & [x,y] in Z )
A42: 1 <= len c by A29, A30, XXREAL_0:2;
then  len c in dom c by FINSEQ_3:25;
then reconsider e = c . (len c) as Element of rc by FUNCT_1:def_3;
A43: 1 <= len c by A29, A30, XXREAL_0:2;
A44: ( e in rc & vs . 1 = vs . ((len c) + 1) ) by A1, A5, MSSCYC_1:6;
thus  ex y being set st
( y in [:{0},(Edges_In (v,rc)):] \/ [:{1},(Edges_Out (v,rc)):] & [x,y] in Z ) ::_thesis: verum
proof
percases ( the Target of G . (c . (len c)) = vs . ((len c) + 1) or ( the Source of G . (c . (len c)) = vs . ((len c) + 1) & the Target of G . (c . (len c)) <> the Source of G . (c . (len c)) ) ) by A1, A42, Lm3;
supposeA45: the Target of G . (c . (len c)) = vs . ((len c) + 1) ; ::_thesis: ex y being set st
( y in [:{0},(Edges_In (v,rc)):] \/ [:{1},(Edges_Out (v,rc)):] & [x,y] in Z )
take y = [0,(c . (len c))]; ::_thesis: ( y in [:{0},(Edges_In (v,rc)):] \/ [:{1},(Edges_Out (v,rc)):] & [x,y] in Z )
 e in Edges_In (v,rc) by A16, A31, A41, A44, A45, Def1;
then A46: y in [:{0},(Edges_In (v,rc)):] by A24, ZFMISC_1:87;
hence  y in [:{0},(Edges_In (v,rc)):] \/ [:{1},(Edges_Out (v,rc)):] by XBOOLE_0:def_3; ::_thesis: [x,y] in Z
reconsider y9 = y as Element of evio by A46, XBOOLE_0:def_3;
 S2[x9,y9,1] by A1, A5, A26, A28, A32, A41, A45, MSSCYC_1:6;
hence  [x,y] in Z by A43; ::_thesis: verum
end;
supposeA47: ( the Source of G . (c . (len c)) = vs . ((len c) + 1) & the Target of G . (c . (len c)) <> the Source of G . (c . (len c)) ) ; ::_thesis: ex y being set st
( y in [:{0},(Edges_In (v,rc)):] \/ [:{1},(Edges_Out (v,rc)):] & [x,y] in Z )
take y = [1,(c . (len c))]; ::_thesis: ( y in [:{0},(Edges_In (v,rc)):] \/ [:{1},(Edges_Out (v,rc)):] & [x,y] in Z )
 e in Edges_Out (v,rc) by A16, A31, A41, A44, A47, Def2;
then A48: y in [:{1},(Edges_Out (v,rc)):] by A23, ZFMISC_1:87;
hence  y in [:{0},(Edges_In (v,rc)):] \/ [:{1},(Edges_Out (v,rc)):] by XBOOLE_0:def_3; ::_thesis: [x,y] in Z
reconsider y9 = y as Element of evio by A48, XBOOLE_0:def_3;
 S2[x9,y9,1] by A1, A5, A26, A28, A32, A41, A47, MSSCYC_1:6;
hence  [x,y] in Z by A43; ::_thesis: verum
end;
end;
end;
end;
end;
end;
end;
supposeA49: u = 1 ; ::_thesis: ex y being set st
( y in [:{0},(Edges_In (v,rc)):] \/ [:{1},(Edges_Out (v,rc)):] & [x,y] in Z )
 n in dom c by A29, A30, FINSEQ_3:25;
then reconsider e = c . n as Element of rc by FUNCT_1:def_3;
A50: e in rc ;
thus  ex y being set st
( y in [:{0},(Edges_In (v,rc)):] \/ [:{1},(Edges_Out (v,rc)):] & [x,y] in Z ) ::_thesis: verum
proof
percases ( vs . n = the Source of G . (c . n) or ( vs . n = the Target of G . (c . n) & the Target of G . (c . n) <> the Source of G . (c . n) ) ) by A1, A29, A30, Lm3;
supposeA51: vs . n = the Source of G . (c . n) ; ::_thesis: ex y being set st
( y in [:{0},(Edges_In (v,rc)):] \/ [:{1},(Edges_Out (v,rc)):] & [x,y] in Z )
take y = [1,(c . n)]; ::_thesis: ( y in [:{0},(Edges_In (v,rc)):] \/ [:{1},(Edges_Out (v,rc)):] & [x,y] in Z )
 e in Edges_Out (v,rc) by A16, A31, A50, A51, Def2;
then A52: y in [:{1},(Edges_Out (v,rc)):] by A23, ZFMISC_1:87;
hence  y in [:{0},(Edges_In (v,rc)):] \/ [:{1},(Edges_Out (v,rc)):] by XBOOLE_0:def_3; ::_thesis: [x,y] in Z
reconsider y9 = y as Element of evio by A52, XBOOLE_0:def_3;
 S1[x9,y9,n] by A26, A28, A49, A51;
hence  [x,y] in Z by A29, A30; ::_thesis: verum
end;
supposeA53: ( vs . n = the Target of G . (c . n) & the Target of G . (c . n) <> the Source of G . (c . n) ) ; ::_thesis: ex y being set st
( y in [:{0},(Edges_In (v,rc)):] \/ [:{1},(Edges_Out (v,rc)):] & [x,y] in Z )
take y = [0,(c . n)]; ::_thesis: ( y in [:{0},(Edges_In (v,rc)):] \/ [:{1},(Edges_Out (v,rc)):] & [x,y] in Z )
 e in Edges_In (v,rc) by A16, A31, A50, A53, Def1;
then A54: y in [:{0},(Edges_In (v,rc)):] by A24, ZFMISC_1:87;
hence  y in [:{0},(Edges_In (v,rc)):] \/ [:{1},(Edges_Out (v,rc)):] by XBOOLE_0:def_3; ::_thesis: [x,y] in Z
reconsider y9 = y as Element of evio by A54, XBOOLE_0:def_3;
 S1[x9,y9,n] by A26, A28, A49, A53;
hence  [x,y] in Z by A29, A30; ::_thesis: verum
end;
end;
end;
end;
end;
end;
thus  for y being set st y in [:{0},(Edges_In (v,rc)):] \/ [:{1},(Edges_Out (v,rc)):] holds
ex x being set st
( x in [:2,ev:] & [x,y] in Z ) ::_thesis: for x, y, z, u being set st [x,y] in Z & [z,u] in Z holds
( x = z iff y = u )
proof
let y be set ; ::_thesis: ( y in [:{0},(Edges_In (v,rc)):] \/ [:{1},(Edges_Out (v,rc)):] implies ex x being set st
( x in [:2,ev:] & [x,y] in Z ) )
assume A55: y in [:{0},(Edges_In (v,rc)):] \/ [:{1},(Edges_Out (v,rc)):] ; ::_thesis: ex x being set st
( x in [:2,ev:] & [x,y] in Z )
then reconsider y9 = y as Element of evio ;
percases ( y in [:{0},(Edges_In (v,rc)):] or y in [:{1},(Edges_Out (v,rc)):] ) by A55, XBOOLE_0:def_3;
supposeA56: y in [:{0},(Edges_In (v,rc)):] ; ::_thesis: ex x being set st
( x in [:2,ev:] & [x,y] in Z )
then consider u, e being set  such that
A57: [u,e] = y by RELAT_1:def_1;
A58: e in Edges_In (v,rc) by A56, A57, ZFMISC_1:87;
then A59: the Target of G . e = v by Def1;
 e in rc by A58, Def1;
then consider n being set  such that
A60: n in dom c and
A61: e = c . n by FUNCT_1:def_3;
reconsider n = n as Element of NAT by A60;
A62: dom c = Seg (len c) by FINSEQ_1:def_3;
then A63: 1 <= n by A60, FINSEQ_1:1;
A64: 1 in 2 by CARD_1:50, TARSKI:def_2;
A65: 0 in 2 by CARD_1:50, TARSKI:def_2;
A66: n <= len c by A60, A62, FINSEQ_1:1;
A67: u in {0} by A56, A57, ZFMISC_1:87;
then A68: u = 0 by TARSKI:def_1;
thus  ex x being set st
( x in [:2,ev:] & [x,y] in Z ) ::_thesis: verum
proof
percases ( vs . (n + 1) = the Target of G . (c . n) or ( vs . n = the Target of G . (c . n) & the Target of G . (c . n) <> the Source of G . (c . n) ) ) by A1, A63, A66, Lm3;
supposeA69: vs . (n + 1) = the Target of G . (c . n) ; ::_thesis: ex x being set st
( x in [:2,ev:] & [x,y] in Z )
thus  ex x being set st
( x in [:2,ev:] & [x,y] in Z ) ::_thesis: verum
proof
percases ( n = len c or n < len c ) by A66, XXREAL_0:1;
supposeA70: n = len c ; ::_thesis: ex x being set st
( x in [:2,ev:] & [x,y] in Z )
take x = [0,1]; ::_thesis: ( x in [:2,ev:] & [x,y] in Z )
 vs . 1 = v by A1, A5, A59, A61, A69, A70, MSSCYC_1:6;
then A71: 1 in ev by A63, A70;
hence  x in [:2,ev:] by A65, ZFMISC_1:87; ::_thesis: [x,y] in Z
reconsider x9 = x as Element of [:2,ev:] by A65, A71, ZFMISC_1:87;
 ( 1 <= len c & S2[x9,y9,1] ) by A1, A5, A57, A67, A60, A61, A62, A69, A70, FINSEQ_1:1, MSSCYC_1:6, TARSKI:def_1;
hence  [x,y] in Z ; ::_thesis: verum
end;
supposeA72: n < len c ; ::_thesis: ex x being set st
( x in [:2,ev:] & [x,y] in Z )
take x = [0,(n + 1)]; ::_thesis: ( x in [:2,ev:] & [x,y] in Z )
A73: ( 1 <= n + 1 & n + 1 <= len c ) by A72, NAT_1:11, NAT_1:13;
then A74: n + 1 in ev by A59, A61, A69;
hence  x in [:2,ev:] by A65, ZFMISC_1:87; ::_thesis: [x,y] in Z
reconsider x9 = x as Element of [:2,ev:] by A65, A74, ZFMISC_1:87;
 S2[x9,y9,n + 1] by A57, A68, A61, A63, A69;
hence  [x,y] in Z by A73; ::_thesis: verum
end;
end;
end;
end;
supposeA75: ( vs . n = the Target of G . (c . n) & the Target of G . (c . n) <> the Source of G . (c . n) ) ; ::_thesis: ex x being set st
( x in [:2,ev:] & [x,y] in Z )
take x = [1,n]; ::_thesis: ( x in [:2,ev:] & [x,y] in Z )
A76: n in ev by A59, A61, A63, A66, A75;
hence  x in [:2,ev:] by A64, ZFMISC_1:87; ::_thesis: [x,y] in Z
reconsider x9 = x as Element of [:2,ev:] by A64, A76, ZFMISC_1:87;
 S1[x9,y9,n] by A57, A67, A61, A75, TARSKI:def_1;
hence  [x,y] in Z by A63, A66; ::_thesis: verum
end;
end;
end;
end;
supposeA77: y in [:{1},(Edges_Out (v,rc)):] ; ::_thesis: ex x being set st
( x in [:2,ev:] & [x,y] in Z )
then consider u, e being set  such that
A78: [u,e] = y by RELAT_1:def_1;
A79: e in Edges_Out (v,rc) by A77, A78, ZFMISC_1:87;
then A80: the Source of G . e = v by Def2;
 e in rc by A79, Def2;
then consider n being set  such that
A81: n in dom c and
A82: e = c . n by FUNCT_1:def_3;
reconsider n = n as Element of NAT by A81;
A83: dom c = Seg (len c) by FINSEQ_1:def_3;
then A84: 1 <= n by A81, FINSEQ_1:1;
A85: 1 in 2 by CARD_1:50, TARSKI:def_2;
A86: 0 in 2 by CARD_1:50, TARSKI:def_2;
A87: n <= len c by A81, A83, FINSEQ_1:1;
A88: u in {1} by A77, A78, ZFMISC_1:87;
then A89: u = 1 by TARSKI:def_1;
thus  ex x being set st
( x in [:2,ev:] & [x,y] in Z ) ::_thesis: verum
proof
percases ( ( vs . (n + 1) = the Source of G . (c . n) & the Target of G . (c . n) <> the Source of G . (c . n) ) or vs . n = the Source of G . (c . n) ) by A1, A84, A87, Lm3;
supposeA90: ( vs . (n + 1) = the Source of G . (c . n) & the Target of G . (c . n) <> the Source of G . (c . n) ) ; ::_thesis: ex x being set st
( x in [:2,ev:] & [x,y] in Z )
thus  ex x being set st
( x in [:2,ev:] & [x,y] in Z ) ::_thesis: verum
proof
percases ( n = len c or n < len c ) by A87, XXREAL_0:1;
supposeA91: n = len c ; ::_thesis: ex x being set st
( x in [:2,ev:] & [x,y] in Z )
take x = [0,1]; ::_thesis: ( x in [:2,ev:] & [x,y] in Z )
 vs . 1 = v by A1, A5, A80, A82, A90, A91, MSSCYC_1:6;
then A92: 1 in ev by A84, A91;
hence  x in [:2,ev:] by A86, ZFMISC_1:87; ::_thesis: [x,y] in Z
reconsider x9 = x as Element of [:2,ev:] by A86, A92, ZFMISC_1:87;
 ( 1 <= len c & S2[x9,y9,1] ) by A1, A5, A78, A88, A81, A82, A83, A90, A91, FINSEQ_1:1, MSSCYC_1:6, TARSKI:def_1;
hence  [x,y] in Z ; ::_thesis: verum
end;
supposeA93: n < len c ; ::_thesis: ex x being set st
( x in [:2,ev:] & [x,y] in Z )
take x = [0,(n + 1)]; ::_thesis: ( x in [:2,ev:] & [x,y] in Z )
A94: ( 1 <= n + 1 & n + 1 <= len c ) by A93, NAT_1:11, NAT_1:13;
then A95: n + 1 in ev by A80, A82, A90;
hence  x in [:2,ev:] by A86, ZFMISC_1:87; ::_thesis: [x,y] in Z
reconsider x9 = x as Element of [:2,ev:] by A86, A95, ZFMISC_1:87;
 S2[x9,y9,n + 1] by A78, A89, A82, A84, A90;
hence  [x,y] in Z by A94; ::_thesis: verum
end;
end;
end;
end;
supposeA96: vs . n = the Source of G . (c . n) ; ::_thesis: ex x being set st
( x in [:2,ev:] & [x,y] in Z )
take x = [1,n]; ::_thesis: ( x in [:2,ev:] & [x,y] in Z )
A97: n in ev by A80, A82, A84, A87, A96;
hence  x in [:2,ev:] by A85, ZFMISC_1:87; ::_thesis: [x,y] in Z
reconsider x9 = x as Element of [:2,ev:] by A85, A97, ZFMISC_1:87;
 S1[x9,y9,n] by A78, A88, A82, A96, TARSKI:def_1;
hence  [x,y] in Z by A84, A87; ::_thesis: verum
end;
end;
end;
end;
end;
end;
thus  for x, y, z, u being set st [x,y] in Z & [z,u] in Z holds
( x = z iff y = u ) ::_thesis: verum
proof
let x, y, z, u be set ; ::_thesis: ( [x,y] in Z & [z,u] in Z implies ( x = z iff y = u ) )
assume that
A98: [x,y] in Z and
A99: [z,u] in Z ; ::_thesis: ( x = z iff y = u )
consider x9 being Element of [:2,ev:], y9 being Element of evio such that
A100: [x,y] = [x9,y9] and
A101: ex n being Element of NAT st
( 1 <= n & n <= len c & ( S2[x9,y9,n] or S1[x9,y9,n] ) ) by A98;
consider z9 being Element of [:2,ev:], u9 being Element of evio such that
A102: [z,u] = [z9,u9] and
A103: ex n being Element of NAT st
( 1 <= n & n <= len c & ( S2[z9,u9,n] or S1[z9,u9,n] ) ) by A99;
A104: x = x9 by A100, XTUPLE_0:1;
A105: y = y9 by A100, XTUPLE_0:1;
consider n2 being Element of NAT  such that
A106: 1 <= n2 and
A107: n2 <= len c and
A108: ( S2[z9,u9,n2] or S1[z9,u9,n2] ) by A103;
consider n1 being Element of NAT  such that
A109: 1 <= n1 and
A110: n1 <= len c and
A111: ( S2[x9,y9,n1] or S1[x9,y9,n1] ) by A101;
A112: z = z9 by A102, XTUPLE_0:1;
thus  ( x = z implies y = u ) ::_thesis: ( y = u implies x = z )
proof
assume A113: x = z ; ::_thesis: y = u
percases ( ( S2[x9,y9,n1] & S2[z9,u9,n2] ) or ( S2[x9,y9,n1] & S1[z9,u9,n2] ) or ( S1[x9,y9,n1] & S2[z9,u9,n2] ) or ( S1[x9,y9,n1] & S1[z9,u9,n2] ) ) by A111, A108;
supposeA114: ( S2[x9,y9,n1] & S2[z9,u9,n2] ) ; ::_thesis: y = u
then A115: n1 = n2 by A104, A112, A113, XTUPLE_0:1;
thus  y = u ::_thesis: verum
proof
percases ( ( ex k being Element of NAT st
( 1 <= k & n1 = k + 1 & ( ( vs . n1 = the Target of G . (c . k) & y9 = [0,(c . k)] ) or ( vs . n1 = the Source of G . (c . k) & y9 = [1,(c . k)] & the Target of G . (c . k) <> the Source of G . (c . k) ) ) ) & ex k being Element of NAT st
( 1 <= k & n2 = k + 1 & ( ( vs . n2 = the Target of G . (c . k) & u9 = [0,(c . k)] ) or ( vs . n2 = the Source of G . (c . k) & u9 = [1,(c . k)] & the Target of G . (c . k) <> the Source of G . (c . k) ) ) ) ) or ( ex k being Element of NAT st
( 1 <= k & n1 = k + 1 & ( ( vs . n1 = the Target of G . (c . k) & y9 = [0,(c . k)] ) or ( vs . n1 = the Source of G . (c . k) & y9 = [1,(c . k)] & the Target of G . (c . k) <> the Source of G . (c . k) ) ) ) & n2 = 1 & ( ( vs . 1 = the Target of G . (c . (len c)) & u9 = [0,(c . (len c))] ) or ( vs . 1 = the Source of G . (c . (len c)) & u9 = [1,(c . (len c))] & the Target of G . (c . (len c)) <> the Source of G . (c . (len c)) ) ) ) or ( n1 = 1 & ( ( vs . 1 = the Target of G . (c . (len c)) & y9 = [0,(c . (len c))] ) or ( vs . 1 = the Source of G . (c . (len c)) & y9 = [1,(c . (len c))] & the Target of G . (c . (len c)) <> the Source of G . (c . (len c)) ) ) & ex k being Element of NAT st
( 1 <= k & n2 = k + 1 & ( ( vs . n2 = the Target of G . (c . k) & u9 = [0,(c . k)] ) or ( vs . n2 = the Source of G . (c . k) & u9 = [1,(c . k)] & the Target of G . (c . k) <> the Source of G . (c . k) ) ) ) ) or ( n1 = 1 & ( ( vs . 1 = the Target of G . (c . (len c)) & y9 = [0,(c . (len c))] ) or ( vs . 1 = the Source of G . (c . (len c)) & y9 = [1,(c . (len c))] & the Target of G . (c . (len c)) <> the Source of G . (c . (len c)) ) ) & n2 = 1 & ( ( vs . 1 = the Target of G . (c . (len c)) & u9 = [0,(c . (len c))] ) or ( vs . 1 = the Source of G . (c . (len c)) & u9 = [1,(c . (len c))] & the Target of G . (c . (len c)) <> the Source of G . (c . (len c)) ) ) ) ) by A114;
suppose ( ex k being Element of NAT st
( 1 <= k & n1 = k + 1 & ( ( vs . n1 = the Target of G . (c . k) & y9 = [0,(c . k)] ) or ( vs . n1 = the Source of G . (c . k) & y9 = [1,(c . k)] & the Target of G . (c . k) <> the Source of G . (c . k) ) ) ) & ex k being Element of NAT st
( 1 <= k & n2 = k + 1 & ( ( vs . n2 = the Target of G . (c . k) & u9 = [0,(c . k)] ) or ( vs . n2 = the Source of G . (c . k) & u9 = [1,(c . k)] & the Target of G . (c . k) <> the Source of G . (c . k) ) ) ) ) ; ::_thesis: y = u
hence  y = u by A102, A105, A115, XTUPLE_0:1; ::_thesis: verum
end;
suppose ( ex k being Element of NAT st
( 1 <= k & n1 = k + 1 & ( ( vs . n1 = the Target of G . (c . k) & y9 = [0,(c . k)] ) or ( vs . n1 = the Source of G . (c . k) & y9 = [1,(c . k)] & the Target of G . (c . k) <> the Source of G . (c . k) ) ) ) & n2 = 1 & ( ( vs . 1 = the Target of G . (c . (len c)) & u9 = [0,(c . (len c))] ) or ( vs . 1 = the Source of G . (c . (len c)) & u9 = [1,(c . (len c))] & the Target of G . (c . (len c)) <> the Source of G . (c . (len c)) ) ) ) ; ::_thesis: y = u
hence  y = u by A115; ::_thesis: verum
end;
suppose ( n1 = 1 & ( ( vs . 1 = the Target of G . (c . (len c)) & y9 = [0,(c . (len c))] ) or ( vs . 1 = the Source of G . (c . (len c)) & y9 = [1,(c . (len c))] & the Target of G . (c . (len c)) <> the Source of G . (c . (len c)) ) ) & ex k being Element of NAT st
( 1 <= k & n2 = k + 1 & ( ( vs . n2 = the Target of G . (c . k) & u9 = [0,(c . k)] ) or ( vs . n2 = the Source of G . (c . k) & u9 = [1,(c . k)] & the Target of G . (c . k) <> the Source of G . (c . k) ) ) ) ) ; ::_thesis: y = u
hence  y = u by A115; ::_thesis: verum
end;
suppose ( n1 = 1 & ( ( vs . 1 = the Target of G . (c . (len c)) & y9 = [0,(c . (len c))] ) or ( vs . 1 = the Source of G . (c . (len c)) & y9 = [1,(c . (len c))] & the Target of G . (c . (len c)) <> the Source of G . (c . (len c)) ) ) & n2 = 1 & ( ( vs . 1 = the Target of G . (c . (len c)) & u9 = [0,(c . (len c))] ) or ( vs . 1 = the Source of G . (c . (len c)) & u9 = [1,(c . (len c))] & the Target of G . (c . (len c)) <> the Source of G . (c . (len c)) ) ) ) ; ::_thesis: y = u
hence  y = u by A102, A105, XTUPLE_0:1; ::_thesis: verum
end;
end;
end;
end;
suppose ( S2[x9,y9,n1] & S1[z9,u9,n2] ) ; ::_thesis: y = u
hence  y = u by A104, A112, A113, XTUPLE_0:1; ::_thesis: verum
end;
suppose ( S1[x9,y9,n1] & S2[z9,u9,n2] ) ; ::_thesis: y = u
hence  y = u by A104, A112, A113, XTUPLE_0:1; ::_thesis: verum
end;
supposeA116: ( S1[x9,y9,n1] & S1[z9,u9,n2] ) ; ::_thesis: y = u
then  n1 = n2 by A104, A112, A113, XTUPLE_0:1;
hence  y = u by A100, A102, A116, XTUPLE_0:1; ::_thesis: verum
end;
end;
end;
A117: u = u9 by A102, XTUPLE_0:1;
thus  ( y = u implies x = z ) ::_thesis: verum
proof
assume A118: y = u ; ::_thesis: x = z
percases ( ( S2[x9,y9,n1] & S2[z9,u9,n2] ) or ( S2[x9,y9,n1] & S1[z9,u9,n2] ) or ( S1[x9,y9,n1] & S2[z9,u9,n2] ) or ( S1[x9,y9,n1] & S1[z9,u9,n2] ) ) by A111, A108;
supposeA119: ( S2[x9,y9,n1] & S2[z9,u9,n2] ) ; ::_thesis: x = z
thus  x = z ::_thesis: verum
proof
percases ( ( ex k being Element of NAT st
( 1 <= k & n1 = k + 1 & ( ( vs . n1 = the Target of G . (c . k) & y9 = [0,(c . k)] ) or ( vs . n1 = the Source of G . (c . k) & y9 = [1,(c . k)] & the Target of G . (c . k) <> the Source of G . (c . k) ) ) ) & ex k being Element of NAT st
( 1 <= k & n2 = k + 1 & ( ( vs . n2 = the Target of G . (c . k) & u9 = [0,(c . k)] ) or ( vs . n2 = the Source of G . (c . k) & u9 = [1,(c . k)] & the Target of G . (c . k) <> the Source of G . (c . k) ) ) ) ) or ( ex k being Element of NAT st
( 1 <= k & n1 = k + 1 & ( ( vs . n1 = the Target of G . (c . k) & y9 = [0,(c . k)] ) or ( vs . n1 = the Source of G . (c . k) & y9 = [1,(c . k)] & the Target of G . (c . k) <> the Source of G . (c . k) ) ) ) & n2 = 1 & ( ( vs . 1 = the Target of G . (c . (len c)) & u9 = [0,(c . (len c))] ) or ( vs . 1 = the Source of G . (c . (len c)) & u9 = [1,(c . (len c))] & the Target of G . (c . (len c)) <> the Source of G . (c . (len c)) ) ) ) or ( n1 = 1 & ( ( vs . 1 = the Target of G . (c . (len c)) & y9 = [0,(c . (len c))] ) or ( vs . 1 = the Source of G . (c . (len c)) & y9 = [1,(c . (len c))] & the Target of G . (c . (len c)) <> the Source of G . (c . (len c)) ) ) & ex k being Element of NAT st
( 1 <= k & n2 = k + 1 & ( ( vs . n2 = the Target of G . (c . k) & u9 = [0,(c . k)] ) or ( vs . n2 = the Source of G . (c . k) & u9 = [1,(c . k)] & the Target of G . (c . k) <> the Source of G . (c . k) ) ) ) ) or ( n1 = 1 & ( ( vs . 1 = the Target of G . (c . (len c)) & y9 = [0,(c . (len c))] ) or ( vs . 1 = the Source of G . (c . (len c)) & y9 = [1,(c . (len c))] & the Target of G . (c . (len c)) <> the Source of G . (c . (len c)) ) ) & n2 = 1 & ( ( vs . 1 = the Target of G . (c . (len c)) & u9 = [0,(c . (len c))] ) or ( vs . 1 = the Source of G . (c . (len c)) & u9 = [1,(c . (len c))] & the Target of G . (c . (len c)) <> the Source of G . (c . (len c)) ) ) ) ) by A119;
supposeA120: ( ex k being Element of NAT st
( 1 <= k & n1 = k + 1 & ( ( vs . n1 = the Target of G . (c . k) & y9 = [0,(c . k)] ) or ( vs . n1 = the Source of G . (c . k) & y9 = [1,(c . k)] & the Target of G . (c . k) <> the Source of G . (c . k) ) ) ) & ex k being Element of NAT st
( 1 <= k & n2 = k + 1 & ( ( vs . n2 = the Target of G . (c . k) & u9 = [0,(c . k)] ) or ( vs . n2 = the Source of G . (c . k) & u9 = [1,(c . k)] & the Target of G . (c . k) <> the Source of G . (c . k) ) ) ) ) ; ::_thesis: x = z
then consider k2 being Element of NAT  such that
A121: 1 <= k2 and
A122: n2 = k2 + 1 and
A123: ( ( vs . n2 = the Target of G . (c . k2) & u9 = [0,(c . k2)] ) or ( vs . n2 = the Source of G . (c . k2) & u9 = [1,(c . k2)] & the Target of G . (c . k2) <> the Source of G . (c . k2) ) ) ;
 k2 <= n2 by A122, NAT_1:12;
then A124: k2 <= len c by A107, XXREAL_0:2;
consider k1 being Element of NAT  such that
A125: 1 <= k1 and
A126: n1 = k1 + 1 and
A127: ( ( vs . n1 = the Target of G . (c . k1) & y9 = [0,(c . k1)] ) or ( vs . n1 = the Source of G . (c . k1) & y9 = [1,(c . k1)] & the Target of G . (c . k1) <> the Source of G . (c . k1) ) ) by A120;
 k1 <= n1 by A126, NAT_1:12;
then A128: k1 <= len c by A110, XXREAL_0:2;
 c . k1 = c . k2 by A105, A117, A118, A127, A123, XTUPLE_0:1;
then  k1 = k2 by A125, A121, A128, A124, Lm2;
hence  x = z by A100, A102, A119, A126, A122, XTUPLE_0:1; ::_thesis: verum
end;
supposeA129: ( ex k being Element of NAT st
( 1 <= k & n1 = k + 1 & ( ( vs . n1 = the Target of G . (c . k) & y9 = [0,(c . k)] ) or ( vs . n1 = the Source of G . (c . k) & y9 = [1,(c . k)] & the Target of G . (c . k) <> the Source of G . (c . k) ) ) ) & n2 = 1 & ( ( vs . 1 = the Target of G . (c . (len c)) & u9 = [0,(c . (len c))] ) or ( vs . 1 = the Source of G . (c . (len c)) & u9 = [1,(c . (len c))] & the Target of G . (c . (len c)) <> the Source of G . (c . (len c)) ) ) ) ; ::_thesis: x = z
A130: 1 <= len c by A109, A110, XXREAL_0:2;
consider k1 being Element of NAT  such that
A131: 1 <= k1 and
A132: n1 = k1 + 1 and
 ( ( vs . n1 = the Target of G . (c . k1) & y9 = [0,(c . k1)] ) or ( vs . n1 = the Source of G . (c . k1) & y9 = [1,(c . k1)] & the Target of G . (c . k1) <> the Source of G . (c . k1) ) ) by A129;
 k1 <= n1 by A132, NAT_1:12;
then A133: k1 <= len c by A110, XXREAL_0:2;
 c . k1 = c . (len c) by A105, A117, A118, A129, A132, XTUPLE_0:1;
then  (len c) + 1 <= len c by A110, A131, A132, A133, A130, Lm2;
hence  x = z by NAT_1:13; ::_thesis: verum
end;
supposeA134: ( n1 = 1 & ( ( vs . 1 = the Target of G . (c . (len c)) & y9 = [0,(c . (len c))] ) or ( vs . 1 = the Source of G . (c . (len c)) & y9 = [1,(c . (len c))] & the Target of G . (c . (len c)) <> the Source of G . (c . (len c)) ) ) & ex k being Element of NAT st
( 1 <= k & n2 = k + 1 & ( ( vs . n2 = the Target of G . (c . k) & u9 = [0,(c . k)] ) or ( vs . n2 = the Source of G . (c . k) & u9 = [1,(c . k)] & the Target of G . (c . k) <> the Source of G . (c . k) ) ) ) ) ; ::_thesis: x = z
A135: 1 <= len c by A106, A107, XXREAL_0:2;
consider k2 being Element of NAT  such that
A136: 1 <= k2 and
A137: n2 = k2 + 1 and
 ( ( vs . n2 = the Target of G . (c . k2) & u9 = [0,(c . k2)] ) or ( vs . n2 = the Source of G . (c . k2) & u9 = [1,(c . k2)] & the Target of G . (c . k2) <> the Source of G . (c . k2) ) ) by A134;
 k2 <= n2 by A137, NAT_1:12;
then A138: k2 <= len c by A107, XXREAL_0:2;
 c . k2 = c . (len c) by A105, A117, A118, A134, A137, XTUPLE_0:1;
then  (len c) + 1 <= len c by A107, A136, A137, A138, A135, Lm2;
hence  x = z by NAT_1:13; ::_thesis: verum
end;
suppose ( n1 = 1 & ( ( vs . 1 = the Target of G . (c . (len c)) & y9 = [0,(c . (len c))] ) or ( vs . 1 = the Source of G . (c . (len c)) & y9 = [1,(c . (len c))] & the Target of G . (c . (len c)) <> the Source of G . (c . (len c)) ) ) & n2 = 1 & ( ( vs . 1 = the Target of G . (c . (len c)) & u9 = [0,(c . (len c))] ) or ( vs . 1 = the Source of G . (c . (len c)) & u9 = [1,(c . (len c))] & the Target of G . (c . (len c)) <> the Source of G . (c . (len c)) ) ) ) ; ::_thesis: x = z
hence  x = z by A100, A102, A119, XTUPLE_0:1; ::_thesis: verum
end;
end;
end;
end;
supposeA139: ( S2[x9,y9,n1] & S1[z9,u9,n2] ) ; ::_thesis: x = z
thus  x = z ::_thesis: verum
proof
percases ( ex k being Element of NAT st
( 1 <= k & n1 = k + 1 & ( ( vs . n1 = the Target of G . (c . k) & y9 = [0,(c . k)] ) or ( vs . n1 = the Source of G . (c . k) & y9 = [1,(c . k)] & the Target of G . (c . k) <> the Source of G . (c . k) ) ) ) or ( n1 = 1 & ( ( vs . 1 = the Target of G . (c . (len c)) & y9 = [0,(c . (len c))] ) or ( vs . 1 = the Source of G . (c . (len c)) & y9 = [1,(c . (len c))] & the Target of G . (c . (len c)) <> the Source of G . (c . (len c)) ) ) ) ) by A139;
suppose ex k being Element of NAT st
( 1 <= k & n1 = k + 1 & ( ( vs . n1 = the Target of G . (c . k) & y9 = [0,(c . k)] ) or ( vs . n1 = the Source of G . (c . k) & y9 = [1,(c . k)] & the Target of G . (c . k) <> the Source of G . (c . k) ) ) ) ; ::_thesis: x = z
then consider k being Element of NAT  such that
A140: 1 <= k and
A141: n1 = k + 1 and
 ( ( vs . n1 = the Target of G . (c . k) & y9 = [0,(c . k)] ) or ( vs . n1 = the Source of G . (c . k) & y9 = [1,(c . k)] & the Target of G . (c . k) <> the Source of G . (c . k) ) ) ;
 k <= n1 by A141, NAT_1:12;
then A142: k <= len c by A110, XXREAL_0:2;
 c . n2 = c . k by A105, A117, A118, A139, A140, A141, XTUPLE_0:1;
then  n2 = k by A106, A107, A140, A142, Lm2;
hence  x = z by A1, A105, A117, A106, A107, A118, A139, A141, Lm3, XTUPLE_0:1; ::_thesis: verum
end;
supposeA143: ( n1 = 1 & ( ( vs . 1 = the Target of G . (c . (len c)) & y9 = [0,(c . (len c))] ) or ( vs . 1 = the Source of G . (c . (len c)) & y9 = [1,(c . (len c))] & the Target of G . (c . (len c)) <> the Source of G . (c . (len c)) ) ) ) ; ::_thesis: x = z
A144: 1 <= len c by A109, A110, XXREAL_0:2;
 c . n2 = c . (len c) by A105, A117, A118, A139, A143, XTUPLE_0:1;
then A145: n2 = len c by A106, A107, A144, Lm2;
 ( ( vs . n2 = the Target of G . (c . n2) & vs . (n2 + 1) = the Source of G . (c . n2) ) or ( vs . n2 = the Source of G . (c . n2) & vs . (n2 + 1) = the Target of G . (c . n2) ) ) by A1, A106, A107, Lm3;
hence  x = z by A1, A5, A105, A117, A118, A139, A143, A145, MSSCYC_1:6, XTUPLE_0:1; ::_thesis: verum
end;
end;
end;
end;
supposeA146: ( S1[x9,y9,n1] & S2[z9,u9,n2] ) ; ::_thesis: x = z
thus  x = z ::_thesis: verum
proof
percases ( ex k being Element of NAT st
( 1 <= k & n2 = k + 1 & ( ( vs . n2 = the Target of G . (c . k) & u9 = [0,(c . k)] ) or ( vs . n2 = the Source of G . (c . k) & u9 = [1,(c . k)] & the Target of G . (c . k) <> the Source of G . (c . k) ) ) ) or ( n2 = 1 & ( ( vs . 1 = the Target of G . (c . (len c)) & u9 = [0,(c . (len c))] ) or ( vs . 1 = the Source of G . (c . (len c)) & u9 = [1,(c . (len c))] & the Target of G . (c . (len c)) <> the Source of G . (c . (len c)) ) ) ) ) by A146;
suppose ex k being Element of NAT st
( 1 <= k & n2 = k + 1 & ( ( vs . n2 = the Target of G . (c . k) & u9 = [0,(c . k)] ) or ( vs . n2 = the Source of G . (c . k) & u9 = [1,(c . k)] & the Target of G . (c . k) <> the Source of G . (c . k) ) ) ) ; ::_thesis: x = z
then consider k being Element of NAT  such that
A147: 1 <= k and
A148: n2 = k + 1 and
 ( ( vs . n2 = the Target of G . (c . k) & u9 = [0,(c . k)] ) or ( vs . n2 = the Source of G . (c . k) & u9 = [1,(c . k)] & the Target of G . (c . k) <> the Source of G . (c . k) ) ) ;
 k <= n2 by A148, NAT_1:12;
then A149: k <= len c by A107, XXREAL_0:2;
 c . n1 = c . k by A105, A117, A118, A146, A147, A148, XTUPLE_0:1;
then  n1 = k by A109, A110, A147, A149, Lm2;
hence  x = z by A1, A105, A117, A109, A110, A118, A146, A148, Lm3, XTUPLE_0:1; ::_thesis: verum
end;
supposeA150: ( n2 = 1 & ( ( vs . 1 = the Target of G . (c . (len c)) & u9 = [0,(c . (len c))] ) or ( vs . 1 = the Source of G . (c . (len c)) & u9 = [1,(c . (len c))] & the Target of G . (c . (len c)) <> the Source of G . (c . (len c)) ) ) ) ; ::_thesis: x = z
A151: 1 <= len c by A109, A110, XXREAL_0:2;
 c . n1 = c . (len c) by A105, A117, A118, A146, A150, XTUPLE_0:1;
then A152: n1 = len c by A109, A110, A151, Lm2;
 ( ( vs . n1 = the Target of G . (c . n1) & vs . (n1 + 1) = the Source of G . (c . n1) ) or ( vs . n1 = the Source of G . (c . n1) & vs . (n1 + 1) = the Target of G . (c . n1) ) ) by A1, A109, A110, Lm3;
hence  x = z by A1, A5, A105, A117, A118, A146, A150, A152, MSSCYC_1:6, XTUPLE_0:1; ::_thesis: verum
end;
end;
end;
end;
supposeA153: ( S1[x9,y9,n1] & S1[z9,u9,n2] ) ; ::_thesis: x = z
then  c . n1 = c . n2 by A105, A117, A118, XTUPLE_0:1;
then  n1 = n2 by A109, A110, A106, A107, Lm2;
hence  x = z by A100, A102, A153, XTUPLE_0:1; ::_thesis: verum
end;
end;
end;
end;
end;
then  [:2,ev:],[:{0},(Edges_In (v,rc)):] \/ [:{1},(Edges_Out (v,rc)):] are_equipotent by TARSKI:def_6;
then  card [:2,ev:] = card ([:{0},(Edges_In (v,rc)):] \/ [:{1},(Edges_Out (v,rc)):]) by CARD_1:5
.= (card [:{0},(Edges_In (v,rc)):]) + (card [:{1},(Edges_Out (v,rc)):]) by A9, CARD_2:40 ;
then  Degree (v,rc) = (card 2) * (card ev) by A7, A6, CARD_2:46
.= 2 * (card ev) by CARD_1:def_2 ;
hence  Degree (v,(rng c)) is even ; ::_thesis: verum
end;
end;
end;

theorem Th49: :: GRAPH_3:49
for G being finite Graph
for v being Vertex of G
for c being cyclic Path of G holds Degree (v,(rng c)) is even
proof
let G be finite Graph; ::_thesis: for v being Vertex of G
for c being cyclic Path of G holds Degree (v,(rng c)) is even
let v be Vertex of G; ::_thesis: for c being cyclic Path of G holds Degree (v,(rng c)) is even
let c be cyclic Path of G; ::_thesis: Degree (v,(rng c)) is even
percases ( c is empty or not c is empty ) ;
suppose c is empty ; ::_thesis: Degree (v,(rng c)) is even
then reconsider rc = rng c as empty set ;
 Degree (v,rc) = 2 * 0 ;
hence  Degree (v,(rng c)) is even ; ::_thesis: verum
end;
supposeA1: not c is empty ; ::_thesis: Degree (v,(rng c)) is even
consider vs being FinSequence of the carrier of G such that
A2: vs is_vertex_seq_of c by GRAPH_2:33;
thus  Degree (v,(rng c)) is even ::_thesis: verum
proof
percases ( v in rng vs or not v in rng vs ) ;
suppose v in rng vs ; ::_thesis: Degree (v,(rng c)) is even
hence  Degree (v,(rng c)) is even by A2, Lm4; ::_thesis: verum
end;
suppose not v in rng vs ; ::_thesis: Degree (v,(rng c)) is even
then  Degree (v,(rng c)) = 2 * 0 by A1, A2, Th32;
hence  Degree (v,(rng c)) is even ; ::_thesis: verum
end;
end;
end;
end;
end;
end;

theorem Th50: :: GRAPH_3:50
for G being finite Graph
for v being Vertex of G
for vs being FinSequence of the carrier of G
for c being Path of G st not c is cyclic & vs is_vertex_seq_of c holds
( Degree (v,(rng c)) is even iff ( v <> vs . 1 & v <> vs . (len vs) ) )
proof
let G be finite Graph; ::_thesis: for v being Vertex of G
for vs being FinSequence of the carrier of G
for c being Path of G st not c is cyclic & vs is_vertex_seq_of c holds
( Degree (v,(rng c)) is even iff ( v <> vs . 1 & v <> vs . (len vs) ) )
let v be Vertex of G; ::_thesis: for vs being FinSequence of the carrier of G
for c being Path of G st not c is cyclic & vs is_vertex_seq_of c holds
( Degree (v,(rng c)) is even iff ( v <> vs . 1 & v <> vs . (len vs) ) )
let vs be FinSequence of the carrier of G; ::_thesis: for c being Path of G st not c is cyclic & vs is_vertex_seq_of c holds
( Degree (v,(rng c)) is even iff ( v <> vs . 1 & v <> vs . (len vs) ) )
let c be Path of G; ::_thesis: ( not c is cyclic & vs is_vertex_seq_of c implies ( Degree (v,(rng c)) is even iff ( v <> vs . 1 & v <> vs . (len vs) ) ) )
assume that
A1: not c is cyclic and
A2: vs is_vertex_seq_of c ; ::_thesis: ( Degree (v,(rng c)) is even iff ( v <> vs . 1 & v <> vs . (len vs) ) )
 len vs = (len c) + 1 by A2, GRAPH_2:def_6;
then A3: 1 <= len vs by NAT_1:11;
then  ( 1 in dom vs & len vs in dom vs ) by FINSEQ_3:25;
then reconsider v1 = vs . 1, v2 = vs . (len vs) as Vertex of G by FINSEQ_2:11;
A4: v1 <> v2 by A1, A2, MSSCYC_1:def_2;
set G9 = AddNewEdge (v1,v2);
reconsider vs9 = vs as FinSequence of the carrier of (AddNewEdge (v1,v2)) by Def7;
reconsider c9 = c as Path of AddNewEdge (v1,v2) by Th37;
A5: vs9 is_vertex_seq_of c9 by A2, Th36;
reconsider v9 = v, v19 = v1, v29 = v2 as Vertex of (AddNewEdge (v1,v2)) by Def7;
set v219 = <*v29,v19*>;
set vs9e = vs9 ^' <*v29,v19*>;
 len <*v29,v19*> = 2 by FINSEQ_1:44;
then A6: (vs9 ^' <*v29,v19*>) . (len (vs9 ^' <*v29,v19*>)) = <*v29,v19*> . 2 by GRAPH_2:16;
set E = the carrier' of G;
set e = the carrier' of G;
A7: the carrier' of G in { the carrier' of G} by TARSKI:def_1;
 the carrier' of (AddNewEdge (v1,v2)) = the carrier' of G \/ { the carrier' of G} by Def7;
then  the carrier' of G in the carrier' of (AddNewEdge (v1,v2)) by A7, XBOOLE_0:def_3;
then reconsider ep = <* the carrier' of G*> as Path of AddNewEdge (v1,v2) by Th4;
A8: rng ep = { the carrier' of G} by FINSEQ_1:39;
A9: not the carrier' of G in the carrier' of G ;
then  rng ep misses the carrier' of G by A8, ZFMISC_1:50;
then A10: (rng ep) /\ the carrier' of G = {} by XBOOLE_0:def_7;
 ( the Source of (AddNewEdge (v1,v2)) . the carrier' of G = v19 & the Target of (AddNewEdge (v1,v2)) . the carrier' of G = v29 ) by Th34;
then A11: ( vs9 . (len vs9) = <*v29,v19*> . 1 & <*v29,v19*> is_vertex_seq_of ep ) by Th11, FINSEQ_1:44;
A12: rng c c= the carrier' of G by FINSEQ_1:def_4;
then A13: not the carrier' of G in rng c by A9;
 rng c9 misses rng ep
proof
assume  not rng c9 misses rng ep ; ::_thesis: contradiction
then  ex x being set st
( x in rng c9 & x in rng ep ) by XBOOLE_0:3;
hence  contradiction by A13, A8, TARSKI:def_1; ::_thesis: verum
end;
then reconsider c9e = c9 ^ ep as Path of AddNewEdge (v1,v2) by A5, A11, Th6;
A14: vs9 ^' <*v29,v19*> is_vertex_seq_of c9e by A5, A11, GRAPH_2:44;
 (vs9 ^' <*v29,v19*>) . 1 = vs . 1 by A3, GRAPH_2:14;
then  (vs9 ^' <*v29,v19*>) . 1 = (vs9 ^' <*v29,v19*>) . (len (vs9 ^' <*v29,v19*>)) by A6, FINSEQ_1:44;
then reconsider c9e = c9e as cyclic Path of AddNewEdge (v1,v2) by A14, MSSCYC_1:def_2;
 rng c9e = (rng c) \/ (rng ep) by FINSEQ_1:31;
then A15: the carrier' of G in rng c9e by A7, A8, XBOOLE_0:def_3;
A16: (rng c9e) /\ the carrier' of G = ((rng c) \/ (rng ep)) /\ the carrier' of G by FINSEQ_1:31
.= ((rng c) /\ the carrier' of G) \/ {} by A10, XBOOLE_1:23
.= rng c by A12, XBOOLE_1:28 ;
then A17: Degree (v,(rng c9e)) = Degree (v,(rng c)) by Th31;
reconsider dv9 = Degree (v9,(rng c9e)) as even Element of NAT by Th49;
A18: Degree (v9,(rng c9e)) is even by Th49;
percases ( ( v <> v1 & v <> v2 ) or v = v1 or v = v2 ) ;
suppose ( v <> v1 & v <> v2 ) ; ::_thesis: ( Degree (v,(rng c)) is even iff ( v <> vs . 1 & v <> vs . (len vs) ) )
hence  ( Degree (v,(rng c)) is even iff ( v <> vs . 1 & v <> vs . (len vs) ) ) by A18, A17, Th48; ::_thesis: verum
end;
supposeA19: ( v = v1 or v = v2 ) ; ::_thesis: ( Degree (v,(rng c)) is even iff ( v <> vs . 1 & v <> vs . (len vs) ) )
then  Degree (v9,(rng c9e)) = (Degree (v,(rng c9e))) + 1 by A4, A15, Th47;
then  Degree (v,(rng c9e)) = dv9 - 1 ;
hence  ( Degree (v,(rng c)) is even iff ( v <> vs . 1 & v <> vs . (len vs) ) ) by A16, A19, Th31; ::_thesis: verum
end;
end;
end;


definition
let G be Graph;
funcG -CycleSet  ->  FinSequenceSet of the carrier' of G means :Def8: :: GRAPH_3:def 8
 for x being set holds
( x in it iff x is cyclic Path of G );
existence
 ex b1 being FinSequenceSet of the carrier' of G st
for x being set holds
( x in b1 iff x is cyclic Path of G )
proof
defpred S1[ set ] means $1 is cyclic Path of G;
set IT =  {  p where p is Element of the carrier' of G * : S1[p]  }  ;
  {  p where p is Element of the carrier' of G * : S1[p]  }  is Subset of ( the carrier' of G *) from DOMAIN_1:sch_7();
then  for x being set st x in  {  p where p is Element of the carrier' of G * : S1[p]  }  holds
x is FinSequence of the carrier' of G by FINSEQ_1:def_11;
then reconsider IT =  {  p where p is Element of the carrier' of G * : S1[p]  }  as FinSequenceSet of the carrier' of G by FINSEQ_2:def_3;
reconsider p = {} as Path of G by GRAPH_1:14;
set v = the Vertex of G;
reconsider IT = IT as FinSequenceSet of the carrier' of G ;
take  IT ; ::_thesis: for x being set holds
( x in IT iff x is cyclic Path of G )
let x be set ; ::_thesis: ( x in IT iff x is cyclic Path of G )
hereby  ::_thesis: ( x is cyclic Path of G implies x in IT )
assume  x in IT ; ::_thesis: x is cyclic Path of G
then  ex p being Element of the carrier' of G * st
( p = x & p is cyclic Path of G ) ;
hence  x is cyclic Path of G ; ::_thesis: verum
end;
assume A1: x is cyclic Path of G ; ::_thesis: x in IT
then  x is Element of the carrier' of G * by FINSEQ_1:def_11;
hence  x in IT by A1; ::_thesis: verum
end;
uniqueness
 for b1, b2 being FinSequenceSet of the carrier' of G st ( for x being set holds
( x in b1 iff x is cyclic Path of G ) ) & ( for x being set holds
( x in b2 iff x is cyclic Path of G ) ) holds
b1 = b2
proof
let it1, it2 be FinSequenceSet of the carrier' of G; ::_thesis: ( ( for x being set holds
( x in it1 iff x is cyclic Path of G ) ) & ( for x being set holds
( x in it2 iff x is cyclic Path of G ) ) implies it1 = it2 )
assume that
A2: for x being set holds
( x in it1 iff x is cyclic Path of G ) and
A3: for x being set holds
( x in it2 iff x is cyclic Path of G ) ; ::_thesis: it1 = it2
now__::_thesis:_for_x_being_set_holds_
(_x_in_it1_iff_x_in_it2_)
let x be set ; ::_thesis: ( x in it1 iff x in it2 )
 ( x in it1 iff x is cyclic Path of G ) by A2;
hence  ( x in it1 iff x in it2 ) by A3; ::_thesis: verum
end;
hence  it1 = it2 by TARSKI:1; ::_thesis: verum
end;
end;

:: deftheorem Def8 defines -CycleSet GRAPH_3:def_8_:_
 for G being Graph
for b2 being FinSequenceSet of the carrier' of G holds
( b2 = G -CycleSet iff for x being set holds
( x in b2 iff x is cyclic Path of G ) );

theorem Th51: :: GRAPH_3:51
for G being Graph holds {} in G -CycleSet
proof
let G be Graph; ::_thesis: {} in G -CycleSet
reconsider p = {} as Path of G by GRAPH_1:14;
set v = the Vertex of G;
 ( <* the Vertex of G*> is_vertex_seq_of p & <* the Vertex of G*> . 1 = <* the Vertex of G*> . (len <* the Vertex of G*>) ) by FINSEQ_1:40, GRAPH_2:32;
then  p is cyclic by MSSCYC_1:def_2;
hence  {} in G -CycleSet by Def8; ::_thesis: verum
end;

registration
let G be Graph;
clusterG -CycleSet  ->  non empty ;
coherence
 not G -CycleSet is empty by Th51;
end;

theorem Th52: :: GRAPH_3:52
for G being Graph
for v being Vertex of G
for c being Element of G -CycleSet st v in G -VSet (rng c) holds
{  c9 where c9 is Element of G -CycleSet : ( rng c9 = rng c & ex vs being FinSequence of the carrier of G st
( vs is_vertex_seq_of c9 & vs . 1 = v ) )  }  is non empty Subset of (G -CycleSet)
proof
let G be Graph; ::_thesis: for v being Vertex of G
for c being Element of G -CycleSet st v in G -VSet (rng c) holds
{  c9 where c9 is Element of G -CycleSet : ( rng c9 = rng c & ex vs being FinSequence of the carrier of G st
( vs is_vertex_seq_of c9 & vs . 1 = v ) )  }  is non empty Subset of (G -CycleSet)
let v be Vertex of G; ::_thesis: for c being Element of G -CycleSet st v in G -VSet (rng c) holds
{  c9 where c9 is Element of G -CycleSet : ( rng c9 = rng c & ex vs being FinSequence of the carrier of G st
( vs is_vertex_seq_of c9 & vs . 1 = v ) )  }  is non empty Subset of (G -CycleSet)
let c be Element of G -CycleSet ; ::_thesis: ( v in G -VSet (rng c) implies  {  c9 where c9 is Element of G -CycleSet : ( rng c9 = rng c & ex vs being FinSequence of the carrier of G st
( vs is_vertex_seq_of c9 & vs . 1 = v ) )  }  is non empty Subset of (G -CycleSet) )
set Cset =  {  c9 where c9 is Element of G -CycleSet : ( rng c9 = rng c & ex vs being FinSequence of the carrier of G st
( vs is_vertex_seq_of c9 & vs . 1 = v ) )  }  ;
reconsider c9 = c as cyclic Path of G by Def8;
consider vs being FinSequence of the carrier of G such that
A1: vs is_vertex_seq_of c9 by GRAPH_2:33;
A2: len vs = (len c) + 1 by A1, GRAPH_2:def_6;
assume A3: v in G -VSet (rng c) ; ::_thesis:  {  c9 where c9 is Element of G -CycleSet : ( rng c9 = rng c & ex vs being FinSequence of the carrier of G st
( vs is_vertex_seq_of c9 & vs . 1 = v ) )  }  is non empty Subset of (G -CycleSet)
then A4: ex vv being Vertex of G st
( vv = v & ex e being Element of the carrier' of G st
( e in rng c & ( vv = the Source of G . e or vv = the Target of G . e ) ) ) ;
then  G -VSet (rng c9) = rng vs by A1, GRAPH_2:31, RELAT_1:38;
then consider n being Nat such that
A5: n in dom vs and
A6: vs . n = v by A3, FINSEQ_2:10;
reconsider n = n as Element of NAT by ORDINAL1:def_12;
 dom vs = Seg (len vs) by FINSEQ_1:def_3;
then A7: ( 1 <= n & n <= len vs ) by A5, FINSEQ_1:1;
A8: now__::_thesis:_not__{__c9_where_c9_is_Element_of_G_-CycleSet_:_(_rng_c9_=_rng_c_&_ex_vs_being_FinSequence_of_the_carrier_of_G_st_
(_vs_is_vertex_seq_of_c9_&_vs_._1_=_v_)_)__}__is_empty
percases ( ( 1 = n & n = len vs ) or 1 = n or n = len vs or ( 1 < n & n < len vs ) ) by A7, XXREAL_0:1;
suppose ( 1 = n & n = len vs ) ; ::_thesis: not  {  c9 where c9 is Element of G -CycleSet : ( rng c9 = rng c & ex vs being FinSequence of the carrier of G st
( vs is_vertex_seq_of c9 & vs . 1 = v ) )  }  is empty
then  0 + 1 = (len c) + 1 by A1, GRAPH_2:def_6;
then  c = {} ;
hence  not  {  c9 where c9 is Element of G -CycleSet : ( rng c9 = rng c & ex vs being FinSequence of the carrier of G st
( vs is_vertex_seq_of c9 & vs . 1 = v ) )  }  is empty by A4; ::_thesis: verum
end;
suppose 1 = n ; ::_thesis: not  {  c9 where c9 is Element of G -CycleSet : ( rng c9 = rng c & ex vs being FinSequence of the carrier of G st
( vs is_vertex_seq_of c9 & vs . 1 = v ) )  }  is empty
then  c in  {  c9 where c9 is Element of G -CycleSet : ( rng c9 = rng c & ex vs being FinSequence of the carrier of G st
( vs is_vertex_seq_of c9 & vs . 1 = v ) )  }  by A1, A6;
hence  not  {  c9 where c9 is Element of G -CycleSet : ( rng c9 = rng c & ex vs being FinSequence of the carrier of G st
( vs is_vertex_seq_of c9 & vs . 1 = v ) )  }  is empty ; ::_thesis: verum
end;
suppose n = len vs ; ::_thesis: not  {  c9 where c9 is Element of G -CycleSet : ( rng c9 = rng c & ex vs being FinSequence of the carrier of G st
( vs is_vertex_seq_of c9 & vs . 1 = v ) )  }  is empty
then  vs . 1 = v by A1, A6, MSSCYC_1:6;
then  c in  {  c9 where c9 is Element of G -CycleSet : ( rng c9 = rng c & ex vs being FinSequence of the carrier of G st
( vs is_vertex_seq_of c9 & vs . 1 = v ) )  }  by A1;
hence  not  {  c9 where c9 is Element of G -CycleSet : ( rng c9 = rng c & ex vs being FinSequence of the carrier of G st
( vs is_vertex_seq_of c9 & vs . 1 = v ) )  }  is empty ; ::_thesis: verum
end;
supposeA9: ( 1 < n & n < len vs ) ; ::_thesis: not  {  c9 where c9 is Element of G -CycleSet : ( rng c9 = rng c & ex vs being FinSequence of the carrier of G st
( vs is_vertex_seq_of c9 & vs . 1 = v ) )  }  is empty
set vs2 = (n,(len vs)) -cut vs;
consider m being Element of NAT  such that
A10: n = 1 + m and
A11: 1 <= m by A9, FINSEQ_4:84;
set vs1 = (1,(m + 1)) -cut vs;
A12: 1 <= (m + 1) + 1 by A9, A10, NAT_1:13;
then A13: (len ((1,(m + 1)) -cut vs)) + 1 = (m + 1) + 1 by A9, A10, Lm1;
then A14: ((1,(m + 1)) -cut vs) . 1 = vs . (1 + 0) by A9, A10, A12, Lm1;
reconsider c1 = (1,m) -cut c9, c2 = (n,(len c)) -cut c9 as Path of G by Th5;
A15: n <= len c by A2, A9, NAT_1:13;
then A16: (n,(len vs)) -cut vs is_vertex_seq_of c2 by A1, A2, A9, GRAPH_2:42;
A17: (len ((n,(len vs)) -cut vs)) + n = (len vs) + 1 by A9, GRAPH_2:def_1;
A18: now__::_thesis:_not_len_((n,(len_vs))_-cut_vs)_=_0
assume  len ((n,(len vs)) -cut vs) = 0 ; ::_thesis: contradiction
then  (len vs) + 1 < (len vs) + 0 by A9, A17;
hence  contradiction by XREAL_1:6; ::_thesis: verum
end;
then A19: 1 + 0 <= len ((n,(len vs)) -cut vs) by NAT_1:13;
then consider lv2 being Element of NAT  such that
 0 <= lv2 and
A20: lv2 < len ((n,(len vs)) -cut vs) and
A21: len ((n,(len vs)) -cut vs) = lv2 + 1 by GRAPH_2:1;
reconsider vs21 = ((n,(len vs)) -cut vs) ^' ((1,(m + 1)) -cut vs) as FinSequence of the carrier of G ;
A22: vs21 . 1 = ((n,(len vs)) -cut vs) . (0 + 1) by A19, GRAPH_2:14
.= vs . (n + 0) by A9, A18, GRAPH_2:def_1 ;
A23: m <= m + 1 by NAT_1:11;
then  m <= len c by A10, A15, XXREAL_0:2;
then A24: (1,(m + 1)) -cut vs is_vertex_seq_of c1 by A1, A11, GRAPH_2:42;
A25: ((n,(len vs)) -cut vs) . (len ((n,(len vs)) -cut vs)) = vs . (n + lv2) by A9, A20, A21, GRAPH_2:def_1
.= ((1,(m + 1)) -cut vs) . 1 by A1, A17, A21, A14, MSSCYC_1:6 ;
now__::_thesis:_for_y_being_set_holds_
(_not_y_in_rng_c1_or_not_y_in_rng_c2_)
given y being set  such that A26: y in rng c1 and
A27: y in rng c2 ; ::_thesis: contradiction
consider b being Nat such that
A28: b in dom c2 and
A29: c2 . b = y by A27, FINSEQ_2:10;
A30: ex l being Element of NAT st
( l in dom c9 & c . l = c2 . b & l + 1 = n + b & n <= l & l <= len c ) by A28, Th2;
consider a being Nat such that
A31: a in dom c1 and
A32: c1 . a = y by A26, FINSEQ_2:10;
consider k being Element of NAT  such that
A33: ( k in dom c9 & c . k = c1 . a ) and
 k + 1 = 1 + a and
 1 <= k and
A34: k <= m by A31, Th2;
 k < n by A10, A34, NAT_1:13;
hence  contradiction by A32, A29, A33, A30, FUNCT_1:def_4; ::_thesis: verum
end;
then  rng c1 misses rng c2 by XBOOLE_0:3;
then reconsider c219 = c2 ^ c1 as Path of G by A24, A16, A25, Th6;
A35: vs21 is_vertex_seq_of c219 by A24, A16, A25, GRAPH_2:44;
A36: c = c1 ^ c2 by A10, A15, A23, GRAPH_2:9, XXREAL_0:2;
 1 < len ((1,(m + 1)) -cut vs) by A11, A13, NAT_1:13;
then vs21 . (len vs21) = ((1,(m + 1)) -cut vs) . (len ((1,(m + 1)) -cut vs)) by GRAPH_2:16
.= vs . n by A9, A10, GRAPH_2:12 ;
then reconsider c219 = c219 as cyclic Path of G by A22, A35, MSSCYC_1:def_2;
reconsider c21 = c219 as Element of G -CycleSet by Def8;
rng c21 = (rng c2) \/ (rng c1) by FINSEQ_1:31
.= rng c by A36, FINSEQ_1:31 ;
then  c21 in  {  c9 where c9 is Element of G -CycleSet : ( rng c9 = rng c & ex vs being FinSequence of the carrier of G st
( vs is_vertex_seq_of c9 & vs . 1 = v ) )  }  by A6, A22, A35;
hence  not  {  c9 where c9 is Element of G -CycleSet : ( rng c9 = rng c & ex vs being FinSequence of the carrier of G st
( vs is_vertex_seq_of c9 & vs . 1 = v ) )  }  is empty ; ::_thesis: verum
end;
end;
end;
  {  c9 where c9 is Element of G -CycleSet : ( rng c9 = rng c & ex vs being FinSequence of the carrier of G st
( vs is_vertex_seq_of c9 & vs . 1 = v ) )  }  c= G -CycleSet
proof
let x be set ; :: according to TARSKI:def_3 ::_thesis: ( not x in  {  c9 where c9 is Element of G -CycleSet : ( rng c9 = rng c & ex vs being FinSequence of the carrier of G st
( vs is_vertex_seq_of c9 & vs . 1 = v ) )  }  or x in G -CycleSet )
assume  x in  {  c9 where c9 is Element of G -CycleSet : ( rng c9 = rng c & ex vs being FinSequence of the carrier of G st
( vs is_vertex_seq_of c9 & vs . 1 = v ) )  }  ; ::_thesis: x in G -CycleSet
then  ex c9 being Element of G -CycleSet st
( c9 = x & rng c9 = rng c & ex vs being FinSequence of the carrier of G st
( vs is_vertex_seq_of c9 & vs . 1 = v ) ) ;
hence  x in G -CycleSet ; ::_thesis: verum
end;
hence   {  c9 where c9 is Element of G -CycleSet : ( rng c9 = rng c & ex vs being FinSequence of the carrier of G st
( vs is_vertex_seq_of c9 & vs . 1 = v ) )  }  is non empty Subset of (G -CycleSet) by A8; ::_thesis: verum
end;

definition
let G be Graph;
let v be Vertex of G;
let c be Element of G -CycleSet ;
assume A1: v in G -VSet (rng c) ;
func Rotate (c,v) ->  Element of G -CycleSet  equals :Def9: :: GRAPH_3:def 9
 choose  {  c9 where c9 is Element of G -CycleSet : ( rng c9 = rng c & ex vs being FinSequence of the carrier of G st
( vs is_vertex_seq_of c9 & vs . 1 = v ) )  }  ;
coherence
 choose  {  c9 where c9 is Element of G -CycleSet : ( rng c9 = rng c & ex vs being FinSequence of the carrier of G st
( vs is_vertex_seq_of c9 & vs . 1 = v ) )  }  is Element of G -CycleSet
proof
set Rotated =  {  c9 where c9 is Element of G -CycleSet : ( rng c9 = rng c & ex vs being FinSequence of the carrier of G st
( vs is_vertex_seq_of c9 & vs . 1 = v ) )  }  ;
set IT = choose  {  c9 where c9 is Element of G -CycleSet : ( rng c9 = rng c & ex vs being FinSequence of the carrier of G st
( vs is_vertex_seq_of c9 & vs . 1 = v ) )  }  ;
 not  {  c9 where c9 is Element of G -CycleSet : ( rng c9 = rng c & ex vs being FinSequence of the carrier of G st
( vs is_vertex_seq_of c9 & vs . 1 = v ) )  }  is empty by A1, Th52;
then  choose  {  c9 where c9 is Element of G -CycleSet : ( rng c9 = rng c & ex vs being FinSequence of the carrier of G st
( vs is_vertex_seq_of c9 & vs . 1 = v ) )  }  in  {  c9 where c9 is Element of G -CycleSet : ( rng c9 = rng c & ex vs being FinSequence of the carrier of G st
( vs is_vertex_seq_of c9 & vs . 1 = v ) )  }  ;
then  ex c9 being Element of G -CycleSet st
( choose  {  c9 where c9 is Element of G -CycleSet : ( rng c9 = rng c & ex vs being FinSequence of the carrier of G st
( vs is_vertex_seq_of c9 & vs . 1 = v ) )  }  = c9 & rng c9 = rng c & ex vs being FinSequence of the carrier of G st
( vs is_vertex_seq_of c9 & vs . 1 = v ) ) ;
hence  choose  {  c9 where c9 is Element of G -CycleSet : ( rng c9 = rng c & ex vs being FinSequence of the carrier of G st
( vs is_vertex_seq_of c9 & vs . 1 = v ) )  }  is Element of G -CycleSet ; ::_thesis: verum
end;
end;

:: deftheorem Def9 defines Rotate GRAPH_3:def_9_:_
 for G being Graph
for v being Vertex of G
for c being Element of G -CycleSet st v in G -VSet (rng c) holds
Rotate (c,v) = choose  {  c9 where c9 is Element of G -CycleSet : ( rng c9 = rng c & ex vs being FinSequence of the carrier of G st
( vs is_vertex_seq_of c9 & vs . 1 = v ) )  }  ;

Lm5:  for G being Graph
for c being Element of G -CycleSet
for v being Vertex of G st v in G -VSet (rng c) holds
rng (Rotate (c,v)) = rng c
proof
let G be Graph; ::_thesis: for c being Element of G -CycleSet
for v being Vertex of G st v in G -VSet (rng c) holds
rng (Rotate (c,v)) = rng c
let c be Element of G -CycleSet ; ::_thesis: for v being Vertex of G st v in G -VSet (rng c) holds
rng (Rotate (c,v)) = rng c
let v be Vertex of G; ::_thesis: ( v in G -VSet (rng c) implies rng (Rotate (c,v)) = rng c )
assume A1: v in G -VSet (rng c) ; ::_thesis: rng (Rotate (c,v)) = rng c
then reconsider Rotated =  {  c9 where c9 is Element of G -CycleSet : ( rng c9 = rng c & ex vs being FinSequence of the carrier of G st
( vs is_vertex_seq_of c9 & vs . 1 = v ) )  }  as non empty Subset of (G -CycleSet) by Th52;
 Rotate (c,v) = choose Rotated by A1, Def9;
then  Rotate (c,v) in Rotated ;
then  ex c9 being Element of G -CycleSet st
( Rotate (c,v) = c9 & rng c9 = rng c & ex vs being FinSequence of the carrier of G st
( vs is_vertex_seq_of c9 & vs . 1 = v ) ) ;
hence  rng (Rotate (c,v)) = rng c ; ::_thesis: verum
end;

definition
let G be Graph;
let c1, c2 be Element of G -CycleSet ;
assume that
A1: G -VSet (rng c1) meets G -VSet (rng c2) and
A2: rng c1 misses rng c2 ;
func CatCycles (c1,c2) ->  Element of G -CycleSet  means :Def10: :: GRAPH_3:def 10
 ex v being Vertex of G st
( v = choose ((G -VSet (rng c1)) /\ (G -VSet (rng c2))) & it = (Rotate (c1,v)) ^ (Rotate (c2,v)) );
existence
 ex b1 being Element of G -CycleSet ex v being Vertex of G st
( v = choose ((G -VSet (rng c1)) /\ (G -VSet (rng c2))) & b1 = (Rotate (c1,v)) ^ (Rotate (c2,v)) )
proof
set v = choose ((G -VSet (rng c1)) /\ (G -VSet (rng c2)));
A3: not (G -VSet (rng c1)) /\ (G -VSet (rng c2)) is empty by A1, XBOOLE_0:def_7;
then A4: choose ((G -VSet (rng c1)) /\ (G -VSet (rng c2))) in (G -VSet (rng c1)) /\ (G -VSet (rng c2)) ;
A5: choose ((G -VSet (rng c1)) /\ (G -VSet (rng c2))) in G -VSet (rng c1) by A3, XBOOLE_0:def_4;
A6: choose ((G -VSet (rng c1)) /\ (G -VSet (rng c2))) in G -VSet (rng c2) by A3, XBOOLE_0:def_4;
reconsider v = choose ((G -VSet (rng c1)) /\ (G -VSet (rng c2))) as Vertex of G by A4;
reconsider Rotated2 =  {  c9 where c9 is Element of G -CycleSet : ( rng c9 = rng c2 & ex vs being FinSequence of the carrier of G st
( vs is_vertex_seq_of c9 & vs . 1 = v ) )  }  as non empty Subset of (G -CycleSet) by A6, Th52;
set r2 = Rotate (c2,v);
 Rotate (c2,v) = choose Rotated2 by A6, Def9;
then  Rotate (c2,v) in Rotated2 ;
then consider c99 being Element of G -CycleSet  such that
A7: Rotate (c2,v) = c99 and
A8: rng c99 = rng c2 and
A9: ex vs being FinSequence of the carrier of G st
( vs is_vertex_seq_of c99 & vs . 1 = v ) ;
consider vs2 being FinSequence of the carrier of G such that
A10: vs2 is_vertex_seq_of c99 and
A11: vs2 . 1 = v by A9;
reconsider c92 = c99 as cyclic Path of G by Def8;
A12: Rotate (c2,v) = c92 by A7;
 not rng c2 is empty by A6, Th16;
then  not c99 is empty by A8;
then  0 + 1 < (len c99) + 1 by XREAL_1:6;
then A13: 1 < len vs2 by A10, GRAPH_2:def_6;
A14: vs2 is_vertex_seq_of c92 by A10;
reconsider Rotated1 =  {  c9 where c9 is Element of G -CycleSet : ( rng c9 = rng c1 & ex vs being FinSequence of the carrier of G st
( vs is_vertex_seq_of c9 & vs . 1 = v ) )  }  as non empty Subset of (G -CycleSet) by A5, Th52;
set r1 = Rotate (c1,v);
 Rotate (c1,v) = choose Rotated1 by A5, Def9;
then  Rotate (c1,v) in Rotated1 ;
then consider c9 being Element of G -CycleSet  such that
A15: Rotate (c1,v) = c9 and
A16: rng c9 = rng c1 and
A17: ex vs being FinSequence of the carrier of G st
( vs is_vertex_seq_of c9 & vs . 1 = v ) ;
reconsider c91 = c9 as cyclic Path of G by Def8;
consider vs1 being FinSequence of the carrier of G such that
A18: vs1 is_vertex_seq_of c9 and
A19: vs1 . 1 = v by A17;
 vs1 is_vertex_seq_of c91 by A18;
then A20: vs1 . 1 = vs1 . (len vs1) by MSSCYC_1:6;
set vs12 = vs1 ^' vs2;
 len vs1 = (len c9) + 1 by A18, GRAPH_2:def_6;
then  1 <= len vs1 by NAT_1:11;
then A21: (vs1 ^' vs2) . 1 = vs1 . 1 by GRAPH_2:14
.= vs2 . (len vs2) by A19, A11, A14, MSSCYC_1:6
.= (vs1 ^' vs2) . (len (vs1 ^' vs2)) by A13, GRAPH_2:16 ;
A22: Rotate (c1,v) = c91 by A15;
then reconsider c = (Rotate (c1,v)) ^ (Rotate (c2,v)) as Path of G by A2, A16, A8, A18, A19, A10, A11, A20, A12, Th6;
 vs1 ^' vs2 is_vertex_seq_of c by A18, A19, A10, A11, A20, A22, A12, GRAPH_2:44;
then  c is cyclic by A21, MSSCYC_1:def_2;
then reconsider c = c as Element of G -CycleSet by Def8;
take  c ; ::_thesis: ex v being Vertex of G st
( v = choose ((G -VSet (rng c1)) /\ (G -VSet (rng c2))) & c = (Rotate (c1,v)) ^ (Rotate (c2,v)) )
take  v ; ::_thesis: ( v = choose ((G -VSet (rng c1)) /\ (G -VSet (rng c2))) & c = (Rotate (c1,v)) ^ (Rotate (c2,v)) )
thus  ( v = choose ((G -VSet (rng c1)) /\ (G -VSet (rng c2))) & c = (Rotate (c1,v)) ^ (Rotate (c2,v)) ) ; ::_thesis: verum
end;
correctness
uniqueness
for b1, b2 being Element of G -CycleSet st ex v being Vertex of G st
( v = choose ((G -VSet (rng c1)) /\ (G -VSet (rng c2))) & b1 = (Rotate (c1,v)) ^ (Rotate (c2,v)) ) & ex v being Vertex of G st
( v = choose ((G -VSet (rng c1)) /\ (G -VSet (rng c2))) & b2 = (Rotate (c1,v)) ^ (Rotate (c2,v)) ) holds
b1 = b2;
;
end;

:: deftheorem Def10 defines CatCycles GRAPH_3:def_10_:_
 for G being Graph
for c1, c2 being Element of G -CycleSet st G -VSet (rng c1) meets G -VSet (rng c2) & rng c1 misses rng c2 holds
for b4 being Element of G -CycleSet holds
( b4 = CatCycles (c1,c2) iff ex v being Vertex of G st
( v = choose ((G -VSet (rng c1)) /\ (G -VSet (rng c2))) & b4 = (Rotate (c1,v)) ^ (Rotate (c2,v)) ) );

theorem Th53: :: GRAPH_3:53
for G being Graph
for c1, c2 being Element of G -CycleSet st G -VSet (rng c1) meets G -VSet (rng c2) & rng c1 misses rng c2 & ( c1 <> {} or c2 <> {} ) holds
not CatCycles (c1,c2) is empty
proof
let G be Graph; ::_thesis: for c1, c2 being Element of G -CycleSet st G -VSet (rng c1) meets G -VSet (rng c2) & rng c1 misses rng c2 & ( c1 <> {} or c2 <> {} ) holds
not CatCycles (c1,c2) is empty
let c1, c2 be Element of G -CycleSet ; ::_thesis: ( G -VSet (rng c1) meets G -VSet (rng c2) & rng c1 misses rng c2 & ( c1 <> {} or c2 <> {} ) implies not CatCycles (c1,c2) is empty )
assume that
A1: G -VSet (rng c1) meets G -VSet (rng c2) and
A2: rng c1 misses rng c2 and
A3: ( c1 <> {} or c2 <> {} ) ; ::_thesis: not CatCycles (c1,c2) is empty
consider v being Vertex of G such that
A4: v = choose ((G -VSet (rng c1)) /\ (G -VSet (rng c2))) and
A5: CatCycles (c1,c2) = (Rotate (c1,v)) ^ (Rotate (c2,v)) by A1, A2, Def10;
A6: (G -VSet (rng c1)) /\ (G -VSet (rng c2)) <> {} by A1, XBOOLE_0:def_7;
then A7: v in G -VSet (rng c1) by A4, XBOOLE_0:def_4;
A8: v in G -VSet (rng c2) by A4, A6, XBOOLE_0:def_4;
percases ( c1 <> {} or c2 <> {} ) by A3;
suppose c1 <> {} ; ::_thesis: not CatCycles (c1,c2) is empty
then  rng (Rotate (c1,v)) <> {} by A7, Lm5;
hence  not CatCycles (c1,c2) is empty by A5, FINSEQ_1:35, RELAT_1:38; ::_thesis: verum
end;
suppose c2 <> {} ; ::_thesis: not CatCycles (c1,c2) is empty
then  rng (Rotate (c2,v)) <> {} by A8, Lm5;
hence  not CatCycles (c1,c2) is empty by A5, FINSEQ_1:35, RELAT_1:38; ::_thesis: verum
end;
end;
end;


definition
let G be finite Graph;
let v be Vertex of G;
let X be set ;
assume A1: Degree (v,X) <> 0 ;
funcX -PathSet v ->  non empty FinSequenceSet of the carrier' of G equals :Def11: :: GRAPH_3:def 11
 {  c where c is Element of X * : ( c is Path of G & not c is empty & ex vs being FinSequence of the carrier of G st
( vs is_vertex_seq_of c & vs . 1 = v ) )  }  ;
coherence
  {  c where c is Element of X * : ( c is Path of G & not c is empty & ex vs being FinSequence of the carrier of G st
( vs is_vertex_seq_of c & vs . 1 = v ) )  }  is non empty FinSequenceSet of the carrier' of G
proof
set e = choose (Edges_At (v,X));
set IT =  {  c where c is Element of X * : ( c is Path of G & not c is empty & ex vs being FinSequence of the carrier of G st
( vs is_vertex_seq_of c & vs . 1 = v ) )  }  ;
A2: now__::_thesis:_for_x_being_set_st_x_in__{__c_where_c_is_Element_of_X_*_:_(_c_is_Path_of_G_&_not_c_is_empty_&_ex_vs_being_FinSequence_of_the_carrier_of_G_st_
(_vs_is_vertex_seq_of_c_&_vs_._1_=_v_)_)__}__holds_
x_is_FinSequence_of_the_carrier'_of_G
let x be set ; ::_thesis: ( x in  {  c where c is Element of X * : ( c is Path of G & not c is empty & ex vs being FinSequence of the carrier of G st
( vs is_vertex_seq_of c & vs . 1 = v ) )  }  implies x is FinSequence of the carrier' of G )
assume  x in  {  c where c is Element of X * : ( c is Path of G & not c is empty & ex vs being FinSequence of the carrier of G st
( vs is_vertex_seq_of c & vs . 1 = v ) )  }  ; ::_thesis: x is FinSequence of the carrier' of G
then  ex c being Element of X * st
( x = c & c is Path of G & not c is empty & ex vs being FinSequence of the carrier of G st
( vs is_vertex_seq_of c & vs . 1 = v ) ) ;
hence  x is FinSequence of the carrier' of G ; ::_thesis: verum
end;
A3: not Edges_At (v,X) is empty by A1, Th25;
now__::_thesis:_ex_e9_being_Element_of_X_st_
(_choose_(Edges_At_(v,X))_=_e9_&_e9_in_X_&_e9_in_the_carrier'_of_G_&_(_v_=_the_Target_of_G_._e9_or_v_=_the_Source_of_G_._e9_)_)
percases ( choose (Edges_At (v,X)) in Edges_In (v,X) or choose (Edges_At (v,X)) in Edges_Out (v,X) ) by A3, XBOOLE_0:def_3;
supposeA4: choose (Edges_At (v,X)) in Edges_In (v,X) ; ::_thesis: ex e9 being Element of X st
( choose (Edges_At (v,X)) = e9 & e9 in X & e9 in the carrier' of G & ( v = the Target of G . e9 or v = the Source of G . e9 ) )
then  ( choose (Edges_At (v,X)) in X & the Target of G . (choose (Edges_At (v,X))) = v ) by Def1;
hence  ex e9 being Element of X st
( choose (Edges_At (v,X)) = e9 & e9 in X & e9 in the carrier' of G & ( v = the Target of G . e9 or v = the Source of G . e9 ) ) by A4; ::_thesis: verum
end;
supposeA5: choose (Edges_At (v,X)) in Edges_Out (v,X) ; ::_thesis: ex e9 being Element of X st
( choose (Edges_At (v,X)) = e9 & e9 in X & e9 in the carrier' of G & ( v = the Target of G . e9 or v = the Source of G . e9 ) )
then  ( choose (Edges_At (v,X)) in X & the Source of G . (choose (Edges_At (v,X))) = v ) by Def2;
hence  ex e9 being Element of X st
( choose (Edges_At (v,X)) = e9 & e9 in X & e9 in the carrier' of G & ( v = the Target of G . e9 or v = the Source of G . e9 ) ) by A5; ::_thesis: verum
end;
end;
end;
then consider e9 being Element of X such that
 choose (Edges_At (v,X)) = e9 and
A6: e9 in X and
A7: e9 in the carrier' of G and
A8: ( v = the Target of G . e9 or v = the Source of G . e9 ) ;
reconsider X9 = X as non empty set by A6;
reconsider e9 = e9 as Element of X9 ;
reconsider c = <*e9*> as Element of X * by FINSEQ_1:def_11;
A9: ex vs being FinSequence of the carrier of G st
( vs is_vertex_seq_of c & vs . 1 = v )
proof
set s = the Source of G . e9;
reconsider s = the Source of G . e9 as Vertex of G by A7, FUNCT_2:5;
set t = the Target of G . e9;
reconsider t = the Target of G . e9 as Vertex of G by A7, FUNCT_2:5;
percases ( v = the Target of G . e9 or v = the Source of G . e9 ) by A8;
supposeA10: v = the Target of G . e9 ; ::_thesis: ex vs being FinSequence of the carrier of G st
( vs is_vertex_seq_of c & vs . 1 = v )
take  <*t,s*> ; ::_thesis: ( <*t,s*> is_vertex_seq_of c & <*t,s*> . 1 = v )
thus  ( <*t,s*> is_vertex_seq_of c & <*t,s*> . 1 = v ) by A10, Th11, FINSEQ_1:44; ::_thesis: verum
end;
supposeA11: v = the Source of G . e9 ; ::_thesis: ex vs being FinSequence of the carrier of G st
( vs is_vertex_seq_of c & vs . 1 = v )
take  <*s,t*> ; ::_thesis: ( <*s,t*> is_vertex_seq_of c & <*s,t*> . 1 = v )
thus  ( <*s,t*> is_vertex_seq_of c & <*s,t*> . 1 = v ) by A11, FINSEQ_1:44, MSSCYC_1:4; ::_thesis: verum
end;
end;
end;
 c is Path of G by A7, Th4;
then  c in  {  c where c is Element of X * : ( c is Path of G & not c is empty & ex vs being FinSequence of the carrier of G st
( vs is_vertex_seq_of c & vs . 1 = v ) )  }  by A9;
hence   {  c where c is Element of X * : ( c is Path of G & not c is empty & ex vs being FinSequence of the carrier of G st
( vs is_vertex_seq_of c & vs . 1 = v ) )  }  is non empty FinSequenceSet of the carrier' of G by A2, FINSEQ_2:def_3; ::_thesis: verum
end;
end;

:: deftheorem Def11 defines -PathSet GRAPH_3:def_11_:_
 for G being finite Graph
for v being Vertex of G
for X being set st Degree (v,X) <> 0 holds
X -PathSet v =  {  c where c is Element of X * : ( c is Path of G & not c is empty & ex vs being FinSequence of the carrier of G st
( vs is_vertex_seq_of c & vs . 1 = v ) )  }  ;

theorem Th54: :: GRAPH_3:54
for X being set
for G being finite Graph
for v being Vertex of G
for p being Element of X -PathSet v
for Y being finite set st Y = the carrier' of G & Degree (v,X) <> 0 holds
len p <= card Y
proof
let X be set ; ::_thesis: for G being finite Graph
for v being Vertex of G
for p being Element of X -PathSet v
for Y being finite set st Y = the carrier' of G & Degree (v,X) <> 0 holds
len p <= card Y
let G be finite Graph; ::_thesis: for v being Vertex of G
for p being Element of X -PathSet v
for Y being finite set st Y = the carrier' of G & Degree (v,X) <> 0 holds
len p <= card Y
let v be Vertex of G; ::_thesis: for p being Element of X -PathSet v
for Y being finite set st Y = the carrier' of G & Degree (v,X) <> 0 holds
len p <= card Y
let p be Element of X -PathSet v; ::_thesis: for Y being finite set st Y = the carrier' of G & Degree (v,X) <> 0 holds
len p <= card Y
let Y be finite set ; ::_thesis: ( Y = the carrier' of G & Degree (v,X) <> 0 implies len p <= card Y )
assume that
A1: Y = the carrier' of G and
A2: Degree (v,X) <> 0 ; ::_thesis: len p <= card Y
A3: p in X -PathSet v ;
 X -PathSet v =  {  c where c is Element of X * : ( c is Path of G & not c is empty & ex vs being FinSequence of the carrier of G st
( vs is_vertex_seq_of c & vs . 1 = v ) )  }  by A2, Def11;
then  ex c being Element of X * st
( p = c & c is Path of G & not c is empty & ex vs being FinSequence of the carrier of G st
( vs is_vertex_seq_of c & vs . 1 = v ) ) by A3;
then A4: card (rng p) = len p by FINSEQ_4:62;
 rng p c= Y by A1, FINSEQ_1:def_4;
hence  len p <= card Y by A4, NAT_1:43; ::_thesis: verum
end;

definition
let G be finite Graph;
let v be Vertex of G;
let X be set ;
assume that
A1: for v being Vertex of G holds Degree (v,X) is even and
A2: Degree (v,X) <> 0 ;
funcX -CycleSet v ->  non empty Subset of (G -CycleSet) equals :Def12: :: GRAPH_3:def 12
 {  c where c is Element of G -CycleSet : ( rng c c= X & not c is empty & ex vs being FinSequence of the carrier of G st
( vs is_vertex_seq_of c & vs . 1 = v ) )  }  ;
coherence
  {  c where c is Element of G -CycleSet : ( rng c c= X & not c is empty & ex vs being FinSequence of the carrier of G st
( vs is_vertex_seq_of c & vs . 1 = v ) )  }  is non empty Subset of (G -CycleSet)
proof
reconsider E = the carrier' of G as finite set by GRAPH_1:def_11;
set XL =  {  (len p) where p is Element of X -PathSet v : verum  }  ;
set IT =  {  c where c is Element of G -CycleSet : ( rng c c= X & not c is empty & ex vs being FinSequence of the carrier of G st
( vs is_vertex_seq_of c & vs . 1 = v ) )  }  ;
set p = the Element of X -PathSet v;
A3: len the Element of X -PathSet v in  {  (len p) where p is Element of X -PathSet v : verum  }  ;
A4:  {  (len p) where p is Element of X -PathSet v : verum  }  c= NAT
proof
let x be set ; :: according to TARSKI:def_3 ::_thesis: ( not x in  {  (len p) where p is Element of X -PathSet v : verum  }  or x in NAT )
assume  x in  {  (len p) where p is Element of X -PathSet v : verum  }  ; ::_thesis: x in NAT
then  ex p being Element of X -PathSet v st x = len p ;
hence  x in NAT ; ::_thesis: verum
end;
A5: X -PathSet v =  {  c where c is Element of X * : ( c is Path of G & not c is empty & ex vs being FinSequence of the carrier of G st
( vs is_vertex_seq_of c & vs . 1 = v ) )  }  by A2, Def11;
  {  (len p) where p is Element of X -PathSet v : verum  }  c= Seg (card E)
proof
let x be set ; :: according to TARSKI:def_3 ::_thesis: ( not x in  {  (len p) where p is Element of X -PathSet v : verum  }  or x in Seg (card E) )
assume  x in  {  (len p) where p is Element of X -PathSet v : verum  }  ; ::_thesis: x in Seg (card E)
then consider p being Element of X -PathSet v such that
A6: x = len p ;
 p in X -PathSet v ;
then  ex c being Element of X * st
( p = c & c is Path of G & not c is empty & ex vs being FinSequence of the carrier of G st
( vs is_vertex_seq_of c & vs . 1 = v ) ) by A5;
then A7: 0 + 1 <= len p by NAT_1:13;
 len p <= card E by A2, Th54;
hence  x in Seg (card E) by A6, A7, FINSEQ_1:1; ::_thesis: verum
end;
then reconsider XL =  {  (len p) where p is Element of X -PathSet v : verum  }  as non empty finite Subset of NAT by A3, A4;
set maxl = max XL;
 max XL in XL by XXREAL_2:def_8;
then consider p being Element of X -PathSet v such that
A8: max XL = len p ;
 p in X -PathSet v ;
then consider c being Element of X *  such that
A9: p = c and
A10: c is Path of G and
A11: not c is empty and
A12: ex vs being FinSequence of the carrier of G st
( vs is_vertex_seq_of c & vs . 1 = v ) by A5;
reconsider p = p as Path of G by A9, A10;
A13: rng c c= X by FINSEQ_1:def_4;
now__::_thesis:_p_is_cyclic
set T = the Target of G;
set S = the Source of G;
A14: rng p c= X by A9, FINSEQ_1:def_4;
consider vs being FinSequence of the carrier of G such that
A15: vs is_vertex_seq_of p and
A16: vs . 1 = v by A9, A12;
 len vs = (len p) + 1 by A15, GRAPH_2:def_6;
then A17: 1 <= len vs by NAT_1:11;
then  len vs in dom vs by FINSEQ_3:25;
then reconsider v1 = vs . (len vs) as Vertex of G by FINSEQ_2:11;
assume  not p is cyclic ; ::_thesis: contradiction
then A18: Degree (v1,(rng p)) is odd by A15, Th50;
then  rng p <> X by A1;
then  rng p c< X by A14, XBOOLE_0:def_8;
then  ex xx being set st
( xx in X & not xx in rng p ) by XBOOLE_0:6;
then reconsider Xp = X \ (rng p) as non empty set by XBOOLE_0:def_5;
set e = choose (Edges_At (v1,Xp));
 Degree (v1,Xp) = (Degree (v1,X)) - (Degree (v1,(rng p))) by A14, Th29;
then  Degree (v1,Xp) <> 0 by A1, A18;
then A19: not Edges_At (v1,Xp) is empty by Th25;
A20: now__::_thesis:_ex_e9_being_Element_of_Xp_st_
(_choose_(Edges_At_(v1,Xp))_=_e9_&_e9_in_Xp_&_e9_in_the_carrier'_of_G_&_(_v1_=_the_Target_of_G_._e9_or_v1_=_the_Source_of_G_._e9_)_)
percases ( choose (Edges_At (v1,Xp)) in Edges_In (v1,Xp) or choose (Edges_At (v1,Xp)) in Edges_Out (v1,Xp) ) by A19, XBOOLE_0:def_3;
supposeA21: choose (Edges_At (v1,Xp)) in Edges_In (v1,Xp) ; ::_thesis: ex e9 being Element of Xp st
( choose (Edges_At (v1,Xp)) = e9 & e9 in Xp & e9 in the carrier' of G & ( v1 = the Target of G . e9 or v1 = the Source of G . e9 ) )
then  ( choose (Edges_At (v1,Xp)) in Xp & the Target of G . (choose (Edges_At (v1,Xp))) = v1 ) by Def1;
hence  ex e9 being Element of Xp st
( choose (Edges_At (v1,Xp)) = e9 & e9 in Xp & e9 in the carrier' of G & ( v1 = the Target of G . e9 or v1 = the Source of G . e9 ) ) by A21; ::_thesis: verum
end;
supposeA22: choose (Edges_At (v1,Xp)) in Edges_Out (v1,Xp) ; ::_thesis: ex e9 being Element of Xp st
( choose (Edges_At (v1,Xp)) = e9 & e9 in Xp & e9 in the carrier' of G & ( v1 = the Target of G . e9 or v1 = the Source of G . e9 ) )
then  ( choose (Edges_At (v1,Xp)) in Xp & the Source of G . (choose (Edges_At (v1,Xp))) = v1 ) by Def2;
hence  ex e9 being Element of Xp st
( choose (Edges_At (v1,Xp)) = e9 & e9 in Xp & e9 in the carrier' of G & ( v1 = the Target of G . e9 or v1 = the Source of G . e9 ) ) by A22; ::_thesis: verum
end;
end;
end;
then reconsider ep = <*(choose (Edges_At (v1,Xp)))*> as Path of G by Th4;
reconsider t = the Target of G . (choose (Edges_At (v1,Xp))), s = the Source of G . (choose (Edges_At (v1,Xp))) as Vertex of G by A20, FUNCT_2:5;
now__::_thesis:_for_x_being_set_holds_
(_not_x_in_rng_ep_or_not_x_in_rng_p_)
given x being set  such that A23: x in rng ep and
A24: x in rng p ; ::_thesis: contradiction
 rng ep = {(choose (Edges_At (v1,Xp)))} by FINSEQ_1:38;
then  x in Xp by A20, A23, TARSKI:def_1;
hence  contradiction by A24, XBOOLE_0:def_5; ::_thesis: verum
end;
then A25: rng ep misses rng p by XBOOLE_0:3;
percases ( v1 = the Target of G . (choose (Edges_At (v1,Xp))) or v1 = the Source of G . (choose (Edges_At (v1,Xp))) ) by A20;
supposeA26: v1 = the Target of G . (choose (Edges_At (v1,Xp))) ; ::_thesis: contradiction
reconsider ts = <*t,s*> as FinSequence of the carrier of G ;
A27: vs . (len vs) = ts . 1 by A26, FINSEQ_1:44;
reconsider X9 = X as non empty set by A20;
reconsider vs1 = vs ^' ts as FinSequence of the carrier of G ;
reconsider e9 = choose (Edges_At (v1,Xp)) as Element of X9 by A20;
A28: vs1 . 1 = v by A16, A17, GRAPH_2:14;
A29: ts is_vertex_seq_of ep by Th11;
then reconsider p1 = p ^ ep as Path of G by A15, A25, A27, Th6;
A30: len p1 = (len p) + (len ep) by FINSEQ_1:22
.= (len p) + 1 by FINSEQ_1:39 ;
reconsider p = p as FinSequence of X by A9;
reconsider ep = <*e9*> as FinSequence of X ;
reconsider xp1 = p ^ ep as Element of X * by FINSEQ_1:def_11;
 vs1 is_vertex_seq_of p1 by A15, A29, A27, GRAPH_2:44;
then  xp1 in X -PathSet v by A5, A28;
then reconsider xp1 = xp1 as Element of X -PathSet v ;
 len xp1 in XL ;
then  (len p) + 1 <= (len p) + 0 by A8, A30, XXREAL_2:def_8;
hence  contradiction by XREAL_1:6; ::_thesis: verum
end;
supposeA31: v1 = the Source of G . (choose (Edges_At (v1,Xp))) ; ::_thesis: contradiction
reconsider ts = <*s,t*> as FinSequence of the carrier of G ;
A32: ( ts is_vertex_seq_of ep & vs . (len vs) = ts . 1 ) by A31, FINSEQ_1:44, MSSCYC_1:4;
then reconsider p1 = p ^ ep as Path of G by A15, A25, Th6;
A33: len p1 = (len p) + (len ep) by FINSEQ_1:22
.= (len p) + 1 by FINSEQ_1:39 ;
reconsider X9 = X as non empty set by A20;
reconsider vs1 = vs ^' ts as FinSequence of the carrier of G ;
reconsider e9 = choose (Edges_At (v1,Xp)) as Element of X9 by A20;
A34: vs1 . 1 = v by A16, A17, GRAPH_2:14;
reconsider p = p as FinSequence of X by A9;
reconsider ep = <*e9*> as FinSequence of X ;
reconsider xp1 = p ^ ep as Element of X * by FINSEQ_1:def_11;
 vs1 is_vertex_seq_of p1 by A15, A32, GRAPH_2:44;
then  xp1 in X -PathSet v by A5, A34;
then reconsider xp1 = xp1 as Element of X -PathSet v ;
 len xp1 in XL ;
then  (len p) + 1 <= (len p) + 0 by A8, A33, XXREAL_2:def_8;
hence  contradiction by XREAL_1:6; ::_thesis: verum
end;
end;
end;
then reconsider c = c as Element of G -CycleSet by A9, Def8;
A35: now__::_thesis:_for_c_being_set_st_c_in__{__c_where_c_is_Element_of_G_-CycleSet_:_(_rng_c_c=_X_&_not_c_is_empty_&_ex_vs_being_FinSequence_of_the_carrier_of_G_st_
(_vs_is_vertex_seq_of_c_&_vs_._1_=_v_)_)__}__holds_
c_in_G_-CycleSet
let c be set ; ::_thesis: ( c in  {  c where c is Element of G -CycleSet : ( rng c c= X & not c is empty & ex vs being FinSequence of the carrier of G st
( vs is_vertex_seq_of c & vs . 1 = v ) )  }  implies c in G -CycleSet )
assume  c in  {  c where c is Element of G -CycleSet : ( rng c c= X & not c is empty & ex vs being FinSequence of the carrier of G st
( vs is_vertex_seq_of c & vs . 1 = v ) )  }  ; ::_thesis: c in G -CycleSet
then  ex c9 being Element of G -CycleSet st
( c = c9 & rng c9 c= X & not c9 is empty & ex vs being FinSequence of the carrier of G st
( vs is_vertex_seq_of c9 & vs . 1 = v ) ) ;
hence  c in G -CycleSet ; ::_thesis: verum
end;
 c in  {  c where c is Element of G -CycleSet : ( rng c c= X & not c is empty & ex vs being FinSequence of the carrier of G st
( vs is_vertex_seq_of c & vs . 1 = v ) )  }  by A11, A12, A13;
hence   {  c where c is Element of G -CycleSet : ( rng c c= X & not c is empty & ex vs being FinSequence of the carrier of G st
( vs is_vertex_seq_of c & vs . 1 = v ) )  }  is non empty Subset of (G -CycleSet) by A35, TARSKI:def_3; ::_thesis: verum
end;
end;

:: deftheorem Def12 defines -CycleSet GRAPH_3:def_12_:_
 for G being finite Graph
for v being Vertex of G
for X being set st ( for v being Vertex of G holds Degree (v,X) is even ) & Degree (v,X) <> 0 holds
X -CycleSet v =  {  c where c is Element of G -CycleSet : ( rng c c= X & not c is empty & ex vs being FinSequence of the carrier of G st
( vs is_vertex_seq_of c & vs . 1 = v ) )  }  ;

theorem Th55: :: GRAPH_3:55
for X being set
for G being finite Graph
for v being Vertex of G st Degree (v,X) <> 0 & ( for v being Vertex of G holds Degree (v,X) is even ) holds
for c being Element of X -CycleSet v holds
( not c is empty & rng c c= X & v in G -VSet (rng c) )
proof
let X be set ; ::_thesis: for G being finite Graph
for v being Vertex of G st Degree (v,X) <> 0 & ( for v being Vertex of G holds Degree (v,X) is even ) holds
for c being Element of X -CycleSet v holds
( not c is empty & rng c c= X & v in G -VSet (rng c) )
let G be finite Graph; ::_thesis: for v being Vertex of G st Degree (v,X) <> 0 & ( for v being Vertex of G holds Degree (v,X) is even ) holds
for c being Element of X -CycleSet v holds
( not c is empty & rng c c= X & v in G -VSet (rng c) )
let v be Vertex of G; ::_thesis: ( Degree (v,X) <> 0 & ( for v being Vertex of G holds Degree (v,X) is even ) implies for c being Element of X -CycleSet v holds
( not c is empty & rng c c= X & v in G -VSet (rng c) ) )
assume  ( Degree (v,X) <> 0 & ( for v being Vertex of G holds Degree (v,X) is even ) ) ; ::_thesis: for c being Element of X -CycleSet v holds
( not c is empty & rng c c= X & v in G -VSet (rng c) )
then A1: X -CycleSet v =  {  c9 where c9 is Element of G -CycleSet : ( rng c9 c= X & not c9 is empty & ex vs being FinSequence of the carrier of G st
( vs is_vertex_seq_of c9 & vs . 1 = v ) )  }  by Def12;
let c be Element of X -CycleSet v; ::_thesis: ( not c is empty & rng c c= X & v in G -VSet (rng c) )
 c in X -CycleSet v ;
then consider c9 being Element of G -CycleSet  such that
A2: c = c9 and
A3: rng c9 c= X and
A4: not c9 is empty and
A5: ex vs being FinSequence of the carrier of G st
( vs is_vertex_seq_of c9 & vs . 1 = v ) by A1;
thus  not c is empty by A2, A4; ::_thesis: ( rng c c= X & v in G -VSet (rng c) )
thus  rng c c= X by A2, A3; ::_thesis: v in G -VSet (rng c)
reconsider c9 = c9 as Path of G by Def8;
consider vs being FinSequence of the carrier of G such that
A6: vs is_vertex_seq_of c9 and
A7: vs . 1 = v by A5;
 len vs = (len c9) + 1 by A6, GRAPH_2:def_6;
then  1 <= len vs by NAT_1:11;
then A8: 1 in dom vs by FINSEQ_3:25;
 G -VSet (rng c9) = rng vs by A4, A6, GRAPH_2:31;
hence  v in G -VSet (rng c) by A2, A7, A8, FUNCT_1:def_3; ::_thesis: verum
end;

theorem Th56: :: GRAPH_3:56
for G being connected finite Graph
for c being Element of G -CycleSet st rng c <> the carrier' of G & not c is empty holds
{  v9 where v9 is Vertex of G : ( v9 in G -VSet (rng c) & Degree v9 <> Degree (v9,(rng c)) )  }  is non empty Subset of the carrier of G
proof
let G be connected finite Graph; ::_thesis: for c being Element of G -CycleSet st rng c <> the carrier' of G & not c is empty holds
{  v9 where v9 is Vertex of G : ( v9 in G -VSet (rng c) & Degree v9 <> Degree (v9,(rng c)) )  }  is non empty Subset of the carrier of G
let c be Element of G -CycleSet ; ::_thesis: ( rng c <> the carrier' of G & not c is empty implies  {  v9 where v9 is Vertex of G : ( v9 in G -VSet (rng c) & Degree v9 <> Degree (v9,(rng c)) )  }  is non empty Subset of the carrier of G )
defpred S1[ Vertex of G] means ( $1 in G -VSet (rng c) & Degree $1 <> Degree ($1,(rng c)) );
set X =  {  v9 where v9 is Vertex of G : S1[v9]  }  ;
set T = the Target of G;
set S = the Source of G;
set E = the carrier' of G;
A1: rng c c= the carrier' of G by FINSEQ_1:def_4;
reconsider cp = c as cyclic Path of G by Def8;
assume that
A2: rng c <> the carrier' of G and
A3: not c is empty ; ::_thesis:  {  v9 where v9 is Vertex of G : ( v9 in G -VSet (rng c) & Degree v9 <> Degree (v9,(rng c)) )  }  is non empty Subset of the carrier of G
consider vs being FinSequence of the carrier of G such that
A4: vs is_vertex_seq_of cp by GRAPH_2:33;
A5: G -VSet (rng cp) = rng vs by A3, A4, GRAPH_2:31;
now__::_thesis:_ex_v_being_Vertex_of_G_st_
(_v_in_rng_vs_&_Degree_v_<>_Degree_(v,(rng_c))_)
consider x being set  such that
A6: ( ( x in rng c & not x in the carrier' of G ) or ( x in the carrier' of G & not x in rng c ) ) by A2, TARSKI:1;
reconsider x = x as Element of the carrier' of G by A1, A6;
reconsider v = the Target of G . x as Vertex of G by A1, A6, FUNCT_2:5;
percases ( v in rng vs or not v in rng vs ) ;
supposeA7: v in rng vs ; ::_thesis: ex v being Vertex of G st
( v in rng vs & Degree v <> Degree (v,(rng c)) )
 Degree v <> Degree (v,(rng c)) by A1, A6, Th26;
hence  ex v being Vertex of G st
( v in rng vs & Degree v <> Degree (v,(rng c)) ) by A7; ::_thesis: verum
end;
supposeA8: not v in rng vs ; ::_thesis: ex v being Vertex of G st
( v in rng vs & Degree v <> Degree (v,(rng c)) )
A9: ex e being set st e in rng c by A3, XBOOLE_0:def_1;
then  rng c meets the carrier' of G by A1, XBOOLE_0:3;
then consider v9 being Vertex of G, e being Element of the carrier' of G such that
A10: v9 in rng vs and
A11: ( not e in rng c & ( v9 = the Target of G . e or v9 = the Source of G . e ) ) by A5, A8, Th19;
 Degree v9 <> Degree (v9,(rng c)) by A1, A9, A11, Th26;
hence  ex v being Vertex of G st
( v in rng vs & Degree v <> Degree (v,(rng c)) ) by A10; ::_thesis: verum
end;
end;
end;
then consider v being Vertex of G such that
A12: ( v in rng vs & Degree v <> Degree (v,(rng c)) ) ;
A13:  {  v9 where v9 is Vertex of G : S1[v9]  }  is Subset of the carrier of G from DOMAIN_1:sch_7();
 v in  {  v9 where v9 is Vertex of G : S1[v9]  }  by A5, A12;
hence   {  v9 where v9 is Vertex of G : ( v9 in G -VSet (rng c) & Degree v9 <> Degree (v9,(rng c)) )  }  is non empty Subset of the carrier of G by A13; ::_thesis: verum
end;

definition
let G be connected finite Graph;
let c be Element of G -CycleSet ;
assume that
A1: rng c <> the carrier' of G and
A2: not c is empty ;
func ExtendCycle c ->  Element of G -CycleSet  means :Def13: :: GRAPH_3:def 13
 ex c9 being Element of G -CycleSet ex v being Vertex of G st
( v = choose  {  v9 where v9 is Vertex of G : ( v9 in G -VSet (rng c) & Degree v9 <> Degree (v9,(rng c)) )  }  & c9 = choose (( the carrier' of G \ (rng c)) -CycleSet v) & it = CatCycles (c,c9) );
existence
 ex b1, c9 being Element of G -CycleSet ex v being Vertex of G st
( v = choose  {  v9 where v9 is Vertex of G : ( v9 in G -VSet (rng c) & Degree v9 <> Degree (v9,(rng c)) )  }  & c9 = choose (( the carrier' of G \ (rng c)) -CycleSet v) & b1 = CatCycles (c,c9) )
proof
set X =  {  v9 where v9 is Vertex of G : ( v9 in G -VSet (rng c) & Degree v9 <> Degree (v9,(rng c)) )  }  ;
set v = choose  {  v9 where v9 is Vertex of G : ( v9 in G -VSet (rng c) & Degree v9 <> Degree (v9,(rng c)) )  }  ;
 not  {  v9 where v9 is Vertex of G : ( v9 in G -VSet (rng c) & Degree v9 <> Degree (v9,(rng c)) )  }  is empty by A1, A2, Th56;
then  choose  {  v9 where v9 is Vertex of G : ( v9 in G -VSet (rng c) & Degree v9 <> Degree (v9,(rng c)) )  }  in  {  v9 where v9 is Vertex of G : ( v9 in G -VSet (rng c) & Degree v9 <> Degree (v9,(rng c)) )  }  ;
then  ex v9 being Vertex of G st
( choose  {  v9 where v9 is Vertex of G : ( v9 in G -VSet (rng c) & Degree v9 <> Degree (v9,(rng c)) )  }  = v9 & v9 in G -VSet (rng c) & Degree v9 <> Degree (v9,(rng c)) ) ;
then reconsider v = choose  {  v9 where v9 is Vertex of G : ( v9 in G -VSet (rng c) & Degree v9 <> Degree (v9,(rng c)) )  }  as Vertex of G ;
set E = the carrier' of G;
reconsider E9 = the carrier' of G as finite set by GRAPH_1:def_11;
 rng c c= the carrier' of G by FINSEQ_1:def_4;
then  rng c c< the carrier' of G by A1, XBOOLE_0:def_8;
then  ex xx being set st
( xx in the carrier' of G & not xx in rng c ) by XBOOLE_0:6;
then reconsider Erc = E9 \ (rng c) as non empty finite set by XBOOLE_0:def_5;
set c9 = choose (Erc -CycleSet v);
 choose (Erc -CycleSet v) in Erc -CycleSet v ;
then reconsider c9 = choose (Erc -CycleSet v) as Element of G -CycleSet ;
reconsider IT = CatCycles (c,c9) as Element of G -CycleSet ;
take  IT ; ::_thesis: ex c9 being Element of G -CycleSet ex v being Vertex of G st
( v = choose  {  v9 where v9 is Vertex of G : ( v9 in G -VSet (rng c) & Degree v9 <> Degree (v9,(rng c)) )  }  & c9 = choose (( the carrier' of G \ (rng c)) -CycleSet v) & IT = CatCycles (c,c9) )
take  c9 ; ::_thesis: ex v being Vertex of G st
( v = choose  {  v9 where v9 is Vertex of G : ( v9 in G -VSet (rng c) & Degree v9 <> Degree (v9,(rng c)) )  }  & c9 = choose (( the carrier' of G \ (rng c)) -CycleSet v) & IT = CatCycles (c,c9) )
take  v ; ::_thesis: ( v = choose  {  v9 where v9 is Vertex of G : ( v9 in G -VSet (rng c) & Degree v9 <> Degree (v9,(rng c)) )  }  & c9 = choose (( the carrier' of G \ (rng c)) -CycleSet v) & IT = CatCycles (c,c9) )
thus  ( v = choose  {  v9 where v9 is Vertex of G : ( v9 in G -VSet (rng c) & Degree v9 <> Degree (v9,(rng c)) )  }  & c9 = choose (( the carrier' of G \ (rng c)) -CycleSet v) & IT = CatCycles (c,c9) ) ; ::_thesis: verum
end;
uniqueness
 for b1, b2 being Element of G -CycleSet st ex c9 being Element of G -CycleSet ex v being Vertex of G st
( v = choose  {  v9 where v9 is Vertex of G : ( v9 in G -VSet (rng c) & Degree v9 <> Degree (v9,(rng c)) )  }  & c9 = choose (( the carrier' of G \ (rng c)) -CycleSet v) & b1 = CatCycles (c,c9) ) & ex c9 being Element of G -CycleSet ex v being Vertex of G st
( v = choose  {  v9 where v9 is Vertex of G : ( v9 in G -VSet (rng c) & Degree v9 <> Degree (v9,(rng c)) )  }  & c9 = choose (( the carrier' of G \ (rng c)) -CycleSet v) & b2 = CatCycles (c,c9) ) holds
b1 = b2 ;
end;

:: deftheorem Def13 defines ExtendCycle GRAPH_3:def_13_:_
 for G being connected finite Graph
for c being Element of G -CycleSet st rng c <> the carrier' of G & not c is empty holds
for b3 being Element of G -CycleSet holds
( b3 = ExtendCycle c iff ex c9 being Element of G -CycleSet ex v being Vertex of G st
( v = choose  {  v9 where v9 is Vertex of G : ( v9 in G -VSet (rng c) & Degree v9 <> Degree (v9,(rng c)) )  }  & c9 = choose (( the carrier' of G \ (rng c)) -CycleSet v) & b3 = CatCycles (c,c9) ) );

theorem Th57: :: GRAPH_3:57
for G being connected finite Graph
for c being Element of G -CycleSet st rng c <> the carrier' of G & not c is empty & ( for v being Vertex of G holds Degree v is even ) holds
( not ExtendCycle c is empty & card (rng c) < card (rng (ExtendCycle c)) )
proof
let G be connected finite Graph; ::_thesis: for c being Element of G -CycleSet st rng c <> the carrier' of G & not c is empty & ( for v being Vertex of G holds Degree v is even ) holds
( not ExtendCycle c is empty & card (rng c) < card (rng (ExtendCycle c)) )
let c be Element of G -CycleSet ; ::_thesis: ( rng c <> the carrier' of G & not c is empty & ( for v being Vertex of G holds Degree v is even ) implies ( not ExtendCycle c is empty & card (rng c) < card (rng (ExtendCycle c)) ) )
set E = the carrier' of G;
reconsider E9 = the carrier' of G as finite set by GRAPH_1:def_11;
reconsider ccp = c as cyclic Path of G by Def8;
assume that
A1: rng c <> the carrier' of G and
A2: not c is empty and
A3: for v being Vertex of G holds Degree v is even ; ::_thesis: ( not ExtendCycle c is empty & card (rng c) < card (rng (ExtendCycle c)) )
A4: rng c c= the carrier' of G by FINSEQ_1:def_4;
then  rng c c< the carrier' of G by A1, XBOOLE_0:def_8;
then  ex xx being set st
( xx in the carrier' of G & not xx in rng c ) by XBOOLE_0:6;
then reconsider Erc = E9 \ (rng c) as non empty finite set by XBOOLE_0:def_5;
reconsider X =  {  v9 where v9 is Vertex of G : ( v9 in G -VSet (rng c) & Degree v9 <> Degree (v9,(rng c)) )  }  as non empty set by A1, A2, Th56;
consider c9 being Element of G -CycleSet , v being Vertex of G such that
A5: v = choose X and
A6: c9 = choose (Erc -CycleSet v) and
A7: ExtendCycle c = CatCycles (c,c9) by A1, A2, Def13;
 v in X by A5;
then A8: ex v9 being Vertex of G st
( v = v9 & v9 in G -VSet (rng c) & Degree v9 <> Degree (v9,(rng c)) ) ;
A9: now__::_thesis:_for_v_being_Vertex_of_G_holds_Degree_(v,Erc)_is_even
let v be Vertex of G; ::_thesis: Degree (v,Erc) is even
A10: ( Degree v = Degree (v, the carrier' of G) & Degree v is even ) by A3, Th24;
 ( Degree (v,Erc) = (Degree (v,E9)) - (Degree (v,(rng c))) & Degree (v,(rng ccp)) is even ) by A4, Th29, Th49;
hence  Degree (v,Erc) is even by A10; ::_thesis: verum
end;
 rng c misses the carrier' of G \ (rng c) by XBOOLE_1:79;
then A11: (rng c) /\ ( the carrier' of G \ (rng c)) = {} by XBOOLE_0:def_7;
 Degree (v,Erc) = (Degree (v,E9)) - (Degree (v,(rng c))) by A4, Th29;
then A12: Degree (v,Erc) <> 0 by A8, Th24;
then  rng c9 c= the carrier' of G \ (rng c) by A6, A9, Th55;
then (rng c) /\ (rng c9) = (rng c) /\ (( the carrier' of G \ (rng c)) /\ (rng c9)) by XBOOLE_1:28
.= {} /\ (rng c9) by A11, XBOOLE_1:16
.= {} ;
then A13: rng c misses rng c9 by XBOOLE_0:def_7;
 v in G -VSet (rng c9) by A6, A9, A12, Th55;
then A14: G -VSet (rng c) meets G -VSet (rng c9) by A8, XBOOLE_0:3;
hence  not ExtendCycle c is empty by A2, A7, A13, Th53; ::_thesis: card (rng c) < card (rng (ExtendCycle c))
consider vr being Vertex of G such that
A15: vr = choose ((G -VSet (rng c)) /\ (G -VSet (rng c9))) and
A16: CatCycles (c,c9) = (Rotate (c,vr)) ^ (Rotate (c9,vr)) by A14, A13, Def10;
A17: (G -VSet (rng c)) /\ (G -VSet (rng c9)) <> {} by A14, XBOOLE_0:def_7;
then  vr in G -VSet (rng c9) by A15, XBOOLE_0:def_4;
then A18: rng (Rotate (c9,vr)) = rng c9 by Lm5;
 vr in G -VSet (rng c) by A17, A15, XBOOLE_0:def_4;
then  rng (Rotate (c,vr)) = rng c by Lm5;
then  rng (ExtendCycle c) = (rng c) \/ (rng c9) by A7, A16, A18, FINSEQ_1:31;
then A19: card (rng (ExtendCycle c)) = (card (rng c)) + (card (rng c9)) by A13, CARD_2:40;
 not c9 is empty by A6, A9, A12, Th55;
hence  card (rng c) < card (rng (ExtendCycle c)) by A19, XREAL_1:29; ::_thesis: verum
end;

begin

definition
let G be Graph;
let p be Path of G;
attrp is Eulerian  means :Def14: :: GRAPH_3:def 14
 rng p = the carrier' of G;
end;

:: deftheorem Def14 defines Eulerian GRAPH_3:def_14_:_
 for G being Graph
for p being Path of G holds
( p is Eulerian iff rng p = the carrier' of G );

theorem Th58: :: GRAPH_3:58
for G being connected Graph
for p being Path of G
for vs being FinSequence of the carrier of G st p is Eulerian & vs is_vertex_seq_of p holds
rng vs = the carrier of G
proof
let G be connected Graph; ::_thesis: for p being Path of G
for vs being FinSequence of the carrier of G st p is Eulerian & vs is_vertex_seq_of p holds
rng vs = the carrier of G
let p be Path of G; ::_thesis: for vs being FinSequence of the carrier of G st p is Eulerian & vs is_vertex_seq_of p holds
rng vs = the carrier of G
let vs be FinSequence of the carrier of G; ::_thesis: ( p is Eulerian & vs is_vertex_seq_of p implies rng vs = the carrier of G )
assume that
A1: p is Eulerian and
A2: vs is_vertex_seq_of p and
A3: rng vs <> the carrier of G ; ::_thesis: contradiction
consider x being set  such that
A4: ( ( x in rng vs & not x in the carrier of G ) or ( x in the carrier of G & not x in rng vs ) ) by A3, TARSKI:1;
 vs <> {} by A2, Th3;
then consider y being set  such that
A5: y in rng vs by XBOOLE_0:def_1;
A6: rng vs c= the carrier of G by FINSEQ_1:def_4;
then consider c being Chain of G, vs1 being FinSequence of the carrier of G such that
A7: not c is empty and
A8: ( vs1 is_vertex_seq_of c & vs1 . 1 = x ) and
 vs1 . (len vs1) = y by A4, A5, Th18;
A9: 1 <= len c by A7, NAT_1:14;
A10: rng p = the carrier' of G by A1, Def14;
reconsider c = c as FinSequence of the carrier' of G by MSSCYC_1:def_1;
 1 in dom c by A9, FINSEQ_3:25;
then  c . 1 in the carrier' of G by PARTFUN1:4;
then  ( the Target of G . (c . 1) in rng vs & the Source of G . (c . 1) in rng vs ) by A2, A10, Th15;
hence  contradiction by A6, A4, A8, A9, Lm3; ::_thesis: verum
end;

theorem Th59: :: GRAPH_3:59
for G being connected finite Graph holds
( ex p being cyclic Path of G st p is Eulerian iff for v being Vertex of G holds Degree v is even )
proof
let G be connected finite Graph; ::_thesis: ( ex p being cyclic Path of G st p is Eulerian iff for v being Vertex of G holds Degree v is even )
set E = the carrier' of G;
hereby  ::_thesis: ( ( for v being Vertex of G holds Degree v is even ) implies ex p being cyclic Path of G st p is Eulerian )
given c being cyclic Path of G such that A1: c is Eulerian ; ::_thesis: for v being Vertex of G holds Degree v is even
let v be Vertex of G; ::_thesis: Degree v is even
consider vs being FinSequence of the carrier of G such that
A2: vs is_vertex_seq_of c and
 vs . 1 = vs . (len vs) by MSSCYC_1:def_2;
 rng vs = the carrier of G by A1, A2, Th58;
then A3: Degree (v,(rng c)) is even by A2, Lm4;
 rng c = the carrier' of G by A1, Def14;
hence  Degree v is even by A3, Th24; ::_thesis: verum
end;
assume A4: for v being Vertex of G holds Degree v is even ; ::_thesis: ex p being cyclic Path of G st p is Eulerian
percases ( G is void or not G is void ) ;
supposeA5: G is void ; ::_thesis: ex p being cyclic Path of G st p is Eulerian
 {} is Element of G -CycleSet by Th51;
then reconsider ec = {} as cyclic Path of G by Def8;
take  ec ; ::_thesis: ec is Eulerian
 the carrier' of G is empty by A5;
hence  rng ec = the carrier' of G ; :: according to GRAPH_3:def_14 ::_thesis: verum
end;
suppose not G is void ; ::_thesis: ex p being cyclic Path of G st p is Eulerian
then reconsider G9 = G as non void connected finite Graph ;
reconsider V = choose the carrier of G as Vertex of G9 ;
deffunc H1( Nat, Element of G9 -CycleSet ) ->  Element of G9 -CycleSet = ExtendCycle $2;
 choose ( the carrier' of G -CycleSet V) in the carrier' of G -CycleSet V ;
then reconsider ec = choose ( the carrier' of G -CycleSet V) as Element of G9 -CycleSet ;
consider f being Function of NAT,(G9 -CycleSet) such that
A6: ( f . 0 = ec & ( for n being Nat holds f . (n + 1) = H1(n,f . n) ) ) from NAT_1:sch_12();
A7: now__::_thesis:_for_v_being_Vertex_of_G_holds_Degree_(v,_the_carrier'_of_G)_is_even
let v be Vertex of G; ::_thesis: Degree (v, the carrier' of G) is even
 Degree v = Degree (v, the carrier' of G) by Th24;
hence  Degree (v, the carrier' of G) is even by A4; ::_thesis: verum
end;
 Degree V = Degree (V, the carrier' of G) by Th24;
then A8: Degree (V, the carrier' of G) <> 0 by Th33;
now__::_thesis:_ex_n_being_Element_of_NAT_ex_c_being_Element_of_G9_-CycleSet_st_
(_c_=_f_._n_&_rng_c_=_the_carrier'_of_G_)
defpred S1[ Element of NAT ] means  ex c being Element of G9 -CycleSet st
( not c is empty & c = f . $1 & $1 <= card (rng c) );
reconsider E = the carrier' of G as finite set by GRAPH_1:def_11;
assume A9: for n being Element of NAT
for c being Element of G9 -CycleSet holds
( not c = f . n or not rng c = the carrier' of G ) ; ::_thesis: contradiction
A10: for n being Element of NAT st S1[n] holds
S1[n + 1]
proof
let n be Element of NAT ; ::_thesis: ( S1[n] implies S1[n + 1] )
given c being Element of G9 -CycleSet  such that A11: not c is empty and
A12: c = f . n and
A13: n <= card (rng c) ; ::_thesis: S1[n + 1]
reconsider r = ExtendCycle c as Element of G9 -CycleSet ;
take  r ; ::_thesis: ( not r is empty & r = f . (n + 1) & n + 1 <= card (rng r) )
 rng c <> E by A9, A12;
hence  not r is empty by A4, A11, Th57; ::_thesis: ( r = f . (n + 1) & n + 1 <= card (rng r) )
thus  r = f . (n + 1) by A6, A12; ::_thesis: n + 1 <= card (rng r)
 rng c <> E by A9, A12;
then  n < card (rng r) by A4, A11, A13, Th57, XXREAL_0:2;
hence  n + 1 <= card (rng r) by NAT_1:13; ::_thesis: verum
end;
A14: S1[ 0 ]
proof
take  ec ; ::_thesis: ( not ec is empty & ec = f . 0 & 0 <= card (rng ec) )
thus  not ec is empty by A7, A8, Th55; ::_thesis: ( ec = f . 0 & 0 <= card (rng ec) )
thus  ec = f . 0 by A6; ::_thesis: 0 <= card (rng ec)
thus  0 <= card (rng ec) ; ::_thesis: verum
end;
 for n being Element of NAT holds S1[n] from NAT_1:sch_1(A14, A10);
then consider c being Element of G -CycleSet  such that
 not c is empty and
 c = f . ((card E) + 1) and
A15: (card E) + 1 <= card (rng c) ;
 rng c c= E by FINSEQ_1:def_4;
then  card (rng c) <= card E by NAT_1:43;
then  (card E) + 1 <= (card E) + 0 by A15, XXREAL_0:2;
hence  contradiction by XREAL_1:6; ::_thesis: verum
end;
then consider n being Element of NAT , c being Element of G -CycleSet  such that
 c = f . n and
A16: rng c = the carrier' of G ;
reconsider c = c as cyclic Path of G by Def8;
take  c ; ::_thesis: c is Eulerian
thus  rng c = the carrier' of G by A16; :: according to GRAPH_3:def_14 ::_thesis: verum
end;
end;
end;

theorem :: GRAPH_3:60
for G being connected finite Graph holds
( ex p being Path of G st
( not p is cyclic & p is Eulerian ) iff ex v1, v2 being Vertex of G st
( v1 <> v2 & ( for v being Vertex of G holds
( Degree v is even iff ( v <> v1 & v <> v2 ) ) ) ) )
proof
let G be connected finite Graph; ::_thesis: ( ex p being Path of G st
( not p is cyclic & p is Eulerian ) iff ex v1, v2 being Vertex of G st
( v1 <> v2 & ( for v being Vertex of G holds
( Degree v is even iff ( v <> v1 & v <> v2 ) ) ) ) )
set V = the carrier of G;
set E = the carrier' of G;
A1: now__::_thesis:_not_{_the_carrier'_of_G}_meets_the_carrier'_of_G
assume  { the carrier' of G} meets the carrier' of G ; ::_thesis: contradiction
then consider x being set  such that
A2: x in { the carrier' of G} and
A3: x in the carrier' of G by XBOOLE_0:3;
 x = the carrier' of G by A2, TARSKI:def_1;
hence  contradiction by A3; ::_thesis: verum
end;
hereby  ::_thesis: ( ex v1, v2 being Vertex of G st
( v1 <> v2 & ( for v being Vertex of G holds
( Degree v is even iff ( v <> v1 & v <> v2 ) ) ) ) implies ex p being Path of G st
( not p is cyclic & p is Eulerian ) )
given p being Path of G such that A4: not p is cyclic and
A5: p is Eulerian ; ::_thesis: ex v1, v2 being Vertex of G st
( v1 <> v2 & ( for v being Vertex of G holds
( Degree v is even iff ( v <> v1 & v <> v2 ) ) ) )
consider vs being FinSequence of the carrier of G such that
A6: vs is_vertex_seq_of p by GRAPH_2:33;
 len vs = (len p) + 1 by A6, GRAPH_2:def_6;
then  1 <= len vs by NAT_1:11;
then  ( 1 in dom vs & len vs in dom vs ) by FINSEQ_3:25;
then reconsider v1 = vs . 1, v2 = vs . (len vs) as Vertex of G by FINSEQ_2:11;
take v1 = v1; ::_thesis: ex v2 being Vertex of G st
( v1 <> v2 & ( for v being Vertex of G holds
( Degree v is even iff ( v <> v1 & v <> v2 ) ) ) )
take v2 = v2; ::_thesis: ( v1 <> v2 & ( for v being Vertex of G holds
( Degree v is even iff ( v <> v1 & v <> v2 ) ) ) )
thus  v1 <> v2 by A4, A6, MSSCYC_1:def_2; ::_thesis: for v being Vertex of G holds
( Degree v is even iff ( v <> v1 & v <> v2 ) )
let v be Vertex of G; ::_thesis: ( Degree v is even iff ( v <> v1 & v <> v2 ) )
Degree v = Degree (v, the carrier' of G) by Th24
.= Degree (v,(rng p)) by A5, Def14 ;
hence  ( Degree v is even iff ( v <> v1 & v <> v2 ) ) by A4, A6, Th50; ::_thesis: verum
end;
given v1, v2 being Vertex of G such that A7: v1 <> v2 and
A8: for v being Vertex of G holds
( Degree v is even iff ( v <> v1 & v <> v2 ) ) ; ::_thesis: ex p being Path of G st
( not p is cyclic & p is Eulerian )
set G9 = AddNewEdge (v1,v2);
set E9 = the carrier' of (AddNewEdge (v1,v2));
A9: the carrier' of (AddNewEdge (v1,v2)) = the carrier' of G \/ { the carrier' of G} by Def7;
 the carrier' of G in { the carrier' of G} by TARSKI:def_1;
then A10: the carrier' of G in the carrier' of (AddNewEdge (v1,v2)) by A9, XBOOLE_0:def_3;
A11: the carrier' of G = the carrier' of (AddNewEdge (v1,v2)) /\ the carrier' of G by A9, XBOOLE_1:21;
 for v being Vertex of (AddNewEdge (v1,v2)) holds Degree v is even
proof
let v9 be Vertex of (AddNewEdge (v1,v2)); ::_thesis: Degree v9 is even
reconsider v = v9 as Vertex of G by Def7;
A12: Degree v9 = Degree (v9, the carrier' of (AddNewEdge (v1,v2))) by Th24;
A13: Degree (v, the carrier' of (AddNewEdge (v1,v2))) = Degree (v, the carrier' of G) by A11, Th31;
percases ( ( v9 <> v1 & v9 <> v2 ) or v = v1 or v = v2 ) ;
supposeA14: ( v9 <> v1 & v9 <> v2 ) ; ::_thesis: Degree v9 is even
then  Degree v9 = Degree (v, the carrier' of (AddNewEdge (v1,v2))) by A12, Th48
.= Degree v by A13, Th24 ;
hence  Degree v9 is even by A8, A14; ::_thesis: verum
end;
supposeA15: ( v = v1 or v = v2 ) ; ::_thesis: Degree v9 is even
then reconsider dv = Degree v as odd Element of NAT by A8;
A16: dv + 1 is even ;
Degree v9 = (Degree (v, the carrier' of (AddNewEdge (v1,v2)))) + 1 by A7, A10, A12, A15, Th47
.= (Degree v) + 1 by A13, Th24 ;
hence  Degree v9 is even by A16; ::_thesis: verum
end;
end;
end;
then consider P9 being cyclic Path of AddNewEdge (v1,v2) such that
A17: P9 is Eulerian by Th59;
A18: rng P9 = the carrier' of (AddNewEdge (v1,v2)) by A17, Def14;
then consider n being Nat such that
A19: n in dom P9 and
A20: P9 . n = the carrier' of G by A10, FINSEQ_2:10;
consider p9 being cyclic Path of AddNewEdge (v1,v2) such that
A21: p9 . 1 = P9 . n and
A22: len p9 = len P9 and
A23: rng p9 = rng P9 by A19, Th10;
reconsider p = ((1 + 1),(len p9)) -cut p9 as Path of AddNewEdge (v1,v2) by Th5;
consider vs9 being FinSequence of the carrier of (AddNewEdge (v1,v2)) such that
A24: vs9 is_vertex_seq_of p9 by GRAPH_2:33;
A25: now__::_thesis:_not_the_carrier'_of_G_in_rng_p
assume  the carrier' of G in rng p ; ::_thesis: contradiction
then consider a being Nat such that
A26: a in dom p and
A27: p . a = the carrier' of G by FINSEQ_2:10;
consider k being Element of NAT  such that
A28: k in dom p9 and
A29: p9 . k = p . a and
 k + 1 = (1 + 1) + a and
A30: 1 + 1 <= k and
 k <= len p9 by A26, Th2;
 1 in dom p9 by A28, FINSEQ_5:6, RELAT_1:38;
then  k = 1 by A20, A21, A27, A28, A29, FUNCT_1:def_4;
hence  contradiction by A30; ::_thesis: verum
end;
A31: ( 1 <= n & n <= len P9 ) by A19, FINSEQ_3:25;
then A32: 1 <= len P9 by XXREAL_0:2;
then reconsider p1 = (1,1) -cut p9 as Chain of AddNewEdge (v1,v2) by A22, GRAPH_2:41;
A33: p9 = p1 ^ (((1 + 1),(len p9)) -cut p9) by A31, A22, GRAPH_2:9, XXREAL_0:2;
reconsider vs = ((1 + 1),(len vs9)) -cut vs9 as FinSequence of the carrier of (AddNewEdge (v1,v2)) ;
A34: len vs9 = (len p9) + 1 by A24, GRAPH_2:def_6;
now__::_thesis:_not_len_P9_=_1
consider c being Chain of G, vs being FinSequence of the carrier of G such that
A35: not c is empty and
 vs is_vertex_seq_of c and
 vs . 1 = v1 and
 vs . (len vs) = v2 by A7, Th18;
reconsider c = c as FinSequence of the carrier' of G by MSSCYC_1:def_1;
 1 in dom c by A35, FINSEQ_5:6;
then A36: ( rng c c= the carrier' of G & c . 1 in rng c ) by FINSEQ_1:def_4, FUNCT_1:def_3;
then A37: c . 1 in the carrier' of G ;
 c . 1 in the carrier' of (AddNewEdge (v1,v2)) by A9, A36, XBOOLE_0:def_3;
then consider m being Nat such that
A38: m in dom P9 and
A39: P9 . m = c . 1 by A18, FINSEQ_2:10;
assume A40: len P9 = 1 ; ::_thesis: contradiction
 ( 1 <= m & m <= len P9 ) by A38, FINSEQ_3:25;
then A41: m = 1 by A40, XXREAL_0:1;
 n = 1 by A31, A40, XXREAL_0:1;
hence  contradiction by A20, A37, A39, A41; ::_thesis: verum
end;
then  1 < len P9 by A32, XXREAL_0:1;
then A42: 1 + 1 <= len P9 by NAT_1:13;
then A43: vs is_vertex_seq_of p by A22, A24, A34, GRAPH_2:42;
reconsider vs = vs as FinSequence of the carrier of G by Def7;
reconsider p = p as Path of G by A25, Th45;
take  p ; ::_thesis: ( not p is cyclic & p is Eulerian )
A44: ( the Source of (AddNewEdge (v1,v2)) . the carrier' of G = v1 & the Target of (AddNewEdge (v1,v2)) . the carrier' of G = v2 ) by Th34;
now__::_thesis:_not_vs_._1_=_vs_._(len_vs)
 1 + 1 <= (len p9) + 1 by A42, A22, NAT_1:12;
then A45: 1 + 1 <= (len vs9) + 1 by A34, NAT_1:12;
then A46: (len vs) + (1 + 1) = (len p9) + (1 + 1) by A34, Lm1;
then  0 + 1 <= len vs by A31, A22, XXREAL_0:2;
then consider i being Element of NAT  such that
 0 <= i and
A47: i < len vs and
A48: len vs = i + 1 by GRAPH_2:1;
((len vs) + 1) + 1 = (len vs) + (1 + 1)
.= (len vs9) + 1 by A45, Lm1 ;
then A49: len vs9 = i + (1 + 1) by A48;
A50: vs9 . 1 = vs9 . (len vs9) by A24, MSSCYC_1:6;
A51: ( ( vs9 . 1 = v1 & vs9 . (1 + 1) = v2 ) or ( vs9 . 1 = v2 & vs9 . (1 + 1) = v1 ) ) by A44, A20, A32, A21, A22, A24, Lm3;
assume A52: vs . 1 = vs . (len vs) ; ::_thesis: contradiction
 vs . (0 + 1) = vs9 . ((1 + 1) + 0) by A31, A22, A45, A46, Lm1;
hence  contradiction by A7, A52, A45, A47, A48, A49, A50, A51, Lm1; ::_thesis: verum
end;
hence  not p is cyclic by A43, A25, Th46, MSSCYC_1:6; ::_thesis: p is Eulerian
 ( rng <* the carrier' of G*> = { the carrier' of G} & p1 = <* the carrier' of G*> ) by A20, A32, A21, A22, FINSEQ_1:39, GRAPH_2:6;
then  ( rng p9 = { the carrier' of G} \/ (rng p) & { the carrier' of G} misses rng p ) by A33, FINSEQ_1:31, FINSEQ_3:91;
hence  rng p = the carrier' of G by A9, A18, A23, A1, XBOOLE_1:72; :: according to GRAPH_3:def_14 ::_thesis: verum
end;