:: EUCLID semantic presentation

definition
let c1 be Nat;
func REAL c1 -> FinSequence-DOMAIN of REAL equals :: EUCLID:def 1
a1 -tuples_on REAL ;
coherence
c1 -tuples_on REAL is FinSequence-DOMAIN of REAL
;
end;

:: deftheorem Def1 defines REAL EUCLID:def 1 :
for b1 being Nat holds REAL b1 = b1 -tuples_on REAL ;

definition
func absreal -> Function of REAL , REAL means :Def2: :: EUCLID:def 2
for b1 being real number holds a1 . b1 = abs b1;
existence
ex b1 being Function of REAL , REAL st
for b2 being real number holds b1 . b2 = abs b2
proof end;
uniqueness
for b1, b2 being Function of REAL , REAL st ( for b3 being real number holds b1 . b3 = abs b3 ) & ( for b3 being real number holds b2 . b3 = abs b3 ) holds
b1 = b2
proof end;
end;

:: deftheorem Def2 defines absreal EUCLID:def 2 :
for b1 being Function of REAL , REAL holds
( b1 = absreal iff for b2 being real number holds b1 . b2 = abs b2 );

definition
let c1 be FinSequence of REAL ;
func abs c1 -> FinSequence of REAL equals :: EUCLID:def 3
absreal * a1;
coherence
absreal * c1 is FinSequence of REAL
;
end;

:: deftheorem Def3 defines abs EUCLID:def 3 :
for b1 being FinSequence of REAL holds abs b1 = absreal * b1;

definition
let c1 be Nat;
func 0* c1 -> FinSequence of REAL equals :: EUCLID:def 4
a1 |-> 0;
coherence
c1 |-> 0 is FinSequence of REAL
;
end;

:: deftheorem Def4 defines 0* EUCLID:def 4 :
for b1 being Nat holds 0* b1 = b1 |-> 0;

definition
let c1 be Nat;
redefine func 0* as 0* c1 -> Element of REAL a1;
coherence
0* c1 is Element of REAL c1
;
end;

definition
let c1 be Nat;
let c2 be Element of REAL c1;
redefine func - as - c2 -> Element of REAL a1;
coherence
- c2 is Element of REAL c1
proof end;
end;

definition
let c1 be Nat;
let c2, c3 be Element of REAL c1;
redefine func + as c2 + c3 -> Element of REAL a1;
coherence
c2 + c3 is Element of REAL c1
proof end;
redefine func - as c2 - c3 -> Element of REAL a1;
coherence
c2 - c3 is Element of REAL c1
proof end;
end;

definition
let c1 be Nat;
let c2 be real number ;
let c3 be Element of REAL c1;
redefine func * as c2 * c3 -> Element of REAL a1;
coherence
c2 * c3 is Element of REAL c1
proof end;
end;

definition
let c1 be Nat;
let c2 be Element of REAL c1;
redefine func abs as abs c2 -> Element of a1 -tuples_on REAL ;
coherence
abs c2 is Element of c1 -tuples_on REAL
by FINSEQ_2:133;
end;

definition
let c1 be Nat;
let c2 be Element of REAL c1;
redefine func sqr as sqr c2 -> Element of a1 -tuples_on REAL ;
coherence
sqr c2 is Element of c1 -tuples_on REAL
proof end;
end;

definition
let c1 be FinSequence of REAL ;
func |.c1.| -> Real equals :: EUCLID:def 5
sqrt (Sum (sqr a1));
coherence
sqrt (Sum (sqr c1)) is Real
;
end;

:: deftheorem Def5 defines |. EUCLID:def 5 :
for b1 being FinSequence of REAL holds |.b1.| = sqrt (Sum (sqr b1));

theorem Th1: :: EUCLID:1
canceled;

theorem Th2: :: EUCLID:2
for b1 being Nat
for b2 being Element of REAL b1 holds len b2 = b1 by FINSEQ_2:109;

theorem Th3: :: EUCLID:3
for b1 being Nat
for b2 being Element of REAL b1 holds dom b2 = Seg b1
proof end;

theorem Th4: :: EUCLID:4
for b1, b2 being Nat
for b3 being Element of REAL b1 holds b3 . b2 in REAL
proof end;

theorem Th5: :: EUCLID:5
for b1 being Nat
for b2, b3 being Element of REAL b1 st ( for b4 being Nat st b4 in Seg b1 holds
b2 . b4 = b3 . b4 ) holds
b2 = b3 by FINSEQ_2:139;

Lemma6: for b1 being Nat
for b2 being Element of REAL b1 holds dom (abs b2) = dom b2
proof end;

theorem Th6: :: EUCLID:6
for b1, b2 being Nat
for b3 being real number
for b4 being Element of REAL b1 st b3 = b4 . b2 holds
(abs b4) . b2 = abs b3
proof end;

Lemma8: for b1 being Nat
for b2 being Element of REAL b1 holds sqr (abs b2) = sqr b2
proof end;

theorem Th7: :: EUCLID:7
for b1 being Nat holds abs (0* b1) = b1 |-> 0
proof end;

theorem Th8: :: EUCLID:8
for b1 being Nat
for b2 being Element of REAL b1 holds abs (- b2) = abs b2
proof end;

theorem Th9: :: EUCLID:9
for b1 being Nat
for b2 being real number
for b3 being Element of REAL b1 holds abs (b2 * b3) = (abs b2) * (abs b3)
proof end;

theorem Th10: :: EUCLID:10
for b1 being Nat holds |.(0* b1).| = 0
proof end;

theorem Th11: :: EUCLID:11
for b1 being Nat
for b2 being Element of REAL b1 st |.b2.| = 0 holds
b2 = 0* b1
proof end;

theorem Th12: :: EUCLID:12
for b1 being Nat
for b2 being Element of REAL b1 holds |.b2.| >= 0
proof end;

theorem Th13: :: EUCLID:13
for b1 being Nat
for b2 being Element of REAL b1 holds |.(- b2).| = |.b2.|
proof end;

theorem Th14: :: EUCLID:14
for b1 being Nat
for b2 being real number
for b3 being Element of REAL b1 holds |.(b2 * b3).| = (abs b2) * |.b3.|
proof end;

theorem Th15: :: EUCLID:15
for b1 being Nat
for b2, b3 being Element of REAL b1 holds |.(b2 + b3).| <= |.b2.| + |.b3.|
proof end;

theorem Th16: :: EUCLID:16
for b1 being Nat
for b2, b3 being Element of REAL b1 holds |.(b2 - b3).| <= |.b2.| + |.b3.|
proof end;

theorem Th17: :: EUCLID:17
for b1 being Nat
for b2, b3 being Element of REAL b1 holds |.b2.| - |.b3.| <= |.(b2 + b3).|
proof end;

theorem Th18: :: EUCLID:18
for b1 being Nat
for b2, b3 being Element of REAL b1 holds |.b2.| - |.b3.| <= |.(b2 - b3).|
proof end;

theorem Th19: :: EUCLID:19
for b1 being Nat
for b2, b3 being Element of REAL b1 holds
( |.(b2 - b3).| = 0 iff b2 = b3 )
proof end;

theorem Th20: :: EUCLID:20
for b1 being Nat
for b2, b3 being Element of REAL b1 st b2 <> b3 holds
|.(b2 - b3).| > 0
proof end;

theorem Th21: :: EUCLID:21
for b1 being Nat
for b2, b3 being Element of REAL b1 holds |.(b2 - b3).| = |.(b3 - b2).|
proof end;

theorem Th22: :: EUCLID:22
for b1 being Nat
for b2, b3, b4 being Element of REAL b1 holds |.(b2 - b3).| <= |.(b2 - b4).| + |.(b4 - b3).|
proof end;

definition
let c1 be Nat;
func Pitag_dist c1 -> Function of [:(REAL a1),(REAL a1):], REAL means :Def6: :: EUCLID:def 6
for b1, b2 being Element of REAL a1 holds a2 . b1,b2 = |.(b1 - b2).|;
existence
ex b1 being Function of [:(REAL c1),(REAL c1):], REAL st
for b2, b3 being Element of REAL c1 holds b1 . b2,b3 = |.(b2 - b3).|
proof end;
uniqueness
for b1, b2 being Function of [:(REAL c1),(REAL c1):], REAL st ( for b3, b4 being Element of REAL c1 holds b1 . b3,b4 = |.(b3 - b4).| ) & ( for b3, b4 being Element of REAL c1 holds b2 . b3,b4 = |.(b3 - b4).| ) holds
b1 = b2
proof end;
end;

:: deftheorem Def6 defines Pitag_dist EUCLID:def 6 :
for b1 being Nat
for b2 being Function of [:(REAL b1),(REAL b1):], REAL holds
( b2 = Pitag_dist b1 iff for b3, b4 being Element of REAL b1 holds b2 . b3,b4 = |.(b3 - b4).| );

theorem Th23: :: EUCLID:23
for b1 being Nat
for b2, b3 being Element of REAL b1 holds sqr (b2 - b3) = sqr (b3 - b2)
proof end;

theorem Th24: :: EUCLID:24
for b1 being Nat holds Pitag_dist b1 is_metric_of REAL b1
proof end;

definition
let c1 be Nat;
func Euclid c1 -> strict MetrSpace equals :: EUCLID:def 7
MetrStruct(# (REAL a1),(Pitag_dist a1) #);
coherence
MetrStruct(# (REAL c1),(Pitag_dist c1) #) is strict MetrSpace
proof end;
end;

:: deftheorem Def7 defines Euclid EUCLID:def 7 :
for b1 being Nat holds Euclid b1 = MetrStruct(# (REAL b1),(Pitag_dist b1) #);

registration
let c1 be Nat;
cluster Euclid a1 -> non empty strict ;
coherence
not Euclid c1 is empty
proof end;
end;

definition
let c1 be Nat;
func TOP-REAL c1 -> strict TopSpace equals :: EUCLID:def 8
TopSpaceMetr (Euclid a1);
coherence
TopSpaceMetr (Euclid c1) is strict TopSpace
;
end;

:: deftheorem Def8 defines TOP-REAL EUCLID:def 8 :
for b1 being Nat holds TOP-REAL b1 = TopSpaceMetr (Euclid b1);

registration
let c1 be Nat;
cluster TOP-REAL a1 -> non empty strict ;
coherence
not TOP-REAL c1 is empty
;
end;

theorem Th25: :: EUCLID:25
for b1 being Nat holds the carrier of (TOP-REAL b1) = REAL b1 ;

theorem Th26: :: EUCLID:26
for b1 being Nat
for b2 being Point of (TOP-REAL b1) holds b2 is Function of Seg b1, REAL
proof end;

theorem Th27: :: EUCLID:27
for b1 being Nat
for b2 being Point of (TOP-REAL b1) holds b2 is FinSequence of REAL
proof end;

theorem Th28: :: EUCLID:28
for b1 being Nat
for b2 being Point of (TOP-REAL b1)
for b3 being FinSequence st b3 = b2 holds
len b3 = b1
proof end;

definition
let c1 be Nat;
func 0.REAL c1 -> Point of (TOP-REAL a1) equals :: EUCLID:def 9
0* a1;
coherence
0* c1 is Point of (TOP-REAL c1)
;
end;

:: deftheorem Def9 defines 0.REAL EUCLID:def 9 :
for b1 being Nat holds 0.REAL b1 = 0* b1;

definition
let c1 be Nat;
let c2, c3 be Point of (TOP-REAL c1);
func c2 + c3 -> Point of (TOP-REAL a1) means :Def10: :: EUCLID:def 10
for b1, b2 being Element of REAL a1 st b1 = a2 & b2 = a3 holds
a4 = b1 + b2;
existence
ex b1 being Point of (TOP-REAL c1) st
for b2, b3 being Element of REAL c1 st b2 = c2 & b3 = c3 holds
b1 = b2 + b3
proof end;
uniqueness
for b1, b2 being Point of (TOP-REAL c1) st ( for b3, b4 being Element of REAL c1 st b3 = c2 & b4 = c3 holds
b1 = b3 + b4 ) & ( for b3, b4 being Element of REAL c1 st b3 = c2 & b4 = c3 holds
b2 = b3 + b4 ) holds
b1 = b2
proof end;
commutativity
for b1, b2, b3 being Point of (TOP-REAL c1) st ( for b4, b5 being Element of REAL c1 st b4 = b2 & b5 = b3 holds
b1 = b4 + b5 ) holds
for b4, b5 being Element of REAL c1 st b4 = b3 & b5 = b2 holds
b1 = b4 + b5
;
end;

:: deftheorem Def10 defines + EUCLID:def 10 :
for b1 being Nat
for b2, b3, b4 being Point of (TOP-REAL b1) holds
( b4 = b2 + b3 iff for b5, b6 being Element of REAL b1 st b5 = b2 & b6 = b3 holds
b4 = b5 + b6 );

theorem Th29: :: EUCLID:29
for b1 being Nat
for b2 being Element of REAL b1 holds sqr (abs b2) = sqr b2 by Lemma8;

theorem Th30: :: EUCLID:30
for b1 being Nat
for b2, b3, b4 being Point of (TOP-REAL b1) holds (b2 + b3) + b4 = b2 + (b3 + b4)
proof end;

theorem Th31: :: EUCLID:31
for b1 being Nat
for b2 being Point of (TOP-REAL b1) holds
( (0.REAL b1) + b2 = b2 & b2 + (0.REAL b1) = b2 )
proof end;

definition
let c1 be real number ;
let c2 be Nat;
let c3 be Point of (TOP-REAL c2);
func c1 * c3 -> Point of (TOP-REAL a2) means :Def11: :: EUCLID:def 11
for b1 being Element of REAL a2 st b1 = a3 holds
a4 = a1 * b1;
existence
ex b1 being Point of (TOP-REAL c2) st
for b2 being Element of REAL c2 st b2 = c3 holds
b1 = c1 * b2
proof end;
uniqueness
for b1, b2 being Point of (TOP-REAL c2) st ( for b3 being Element of REAL c2 st b3 = c3 holds
b1 = c1 * b3 ) & ( for b3 being Element of REAL c2 st b3 = c3 holds
b2 = c1 * b3 ) holds
b1 = b2
proof end;
end;

:: deftheorem Def11 defines * EUCLID:def 11 :
for b1 being real number
for b2 being Nat
for b3, b4 being Point of (TOP-REAL b2) holds
( b4 = b1 * b3 iff for b5 being Element of REAL b2 st b5 = b3 holds
b4 = b1 * b5 );

theorem Th32: :: EUCLID:32
for b1 being Nat
for b2 being real number holds b2 * (0.REAL b1) = 0.REAL b1
proof end;

theorem Th33: :: EUCLID:33
for b1 being Nat
for b2 being Point of (TOP-REAL b1) holds
( 1 * b2 = b2 & 0 * b2 = 0.REAL b1 )
proof end;

theorem Th34: :: EUCLID:34
for b1 being Nat
for b2 being Point of (TOP-REAL b1)
for b3, b4 being real number holds (b3 * b4) * b2 = b3 * (b4 * b2)
proof end;

theorem Th35: :: EUCLID:35
for b1 being Nat
for b2 being Point of (TOP-REAL b1)
for b3 being real number holds
( not b3 * b2 = 0.REAL b1 or b3 = 0 or b2 = 0.REAL b1 )
proof end;

theorem Th36: :: EUCLID:36
for b1 being Nat
for b2, b3 being Point of (TOP-REAL b1)
for b4 being real number holds b4 * (b2 + b3) = (b4 * b2) + (b4 * b3)
proof end;

theorem Th37: :: EUCLID:37
for b1 being Nat
for b2 being Point of (TOP-REAL b1)
for b3, b4 being real number holds (b3 + b4) * b2 = (b3 * b2) + (b4 * b2)
proof end;

theorem Th38: :: EUCLID:38
for b1 being Nat
for b2, b3 being Point of (TOP-REAL b1)
for b4 being real number holds
( not b4 * b2 = b4 * b3 or b4 = 0 or b2 = b3 )
proof end;

definition
let c1 be Nat;
let c2 be Point of (TOP-REAL c1);
func - c2 -> Point of (TOP-REAL a1) means :Def12: :: EUCLID:def 12
for b1 being Element of REAL a1 st b1 = a2 holds
a3 = - b1;
existence
ex b1 being Point of (TOP-REAL c1) st
for b2 being Element of REAL c1 st b2 = c2 holds
b1 = - b2
proof end;
uniqueness
for b1, b2 being Point of (TOP-REAL c1) st ( for b3 being Element of REAL c1 st b3 = c2 holds
b1 = - b3 ) & ( for b3 being Element of REAL c1 st b3 = c2 holds
b2 = - b3 ) holds
b1 = b2
proof end;
end;

:: deftheorem Def12 defines - EUCLID:def 12 :
for b1 being Nat
for b2, b3 being Point of (TOP-REAL b1) holds
( b3 = - b2 iff for b4 being Element of REAL b1 st b4 = b2 holds
b3 = - b4 );

theorem Th39: :: EUCLID:39
for b1 being Nat
for b2 being Point of (TOP-REAL b1) holds - (- b2) = b2
proof end;

theorem Th40: :: EUCLID:40
for b1 being Nat
for b2 being Point of (TOP-REAL b1) holds b2 + (- b2) = 0.REAL b1
proof end;

theorem Th41: :: EUCLID:41
for b1 being Nat
for b2, b3 being Point of (TOP-REAL b1) st b2 + b3 = 0.REAL b1 holds
( b2 = - b3 & b3 = - b2 )
proof end;

theorem Th42: :: EUCLID:42
for b1 being Nat
for b2, b3 being Point of (TOP-REAL b1) holds - (b2 + b3) = (- b2) + (- b3)
proof end;

theorem Th43: :: EUCLID:43
for b1 being Nat
for b2 being Point of (TOP-REAL b1) holds - b2 = (- 1) * b2
proof end;

theorem Th44: :: EUCLID:44
for b1 being Nat
for b2 being Point of (TOP-REAL b1)
for b3 being real number holds
( - (b3 * b2) = (- b3) * b2 & - (b3 * b2) = b3 * (- b2) )
proof end;

definition
let c1 be Nat;
let c2, c3 be Point of (TOP-REAL c1);
func c2 - c3 -> Point of (TOP-REAL a1) means :Def13: :: EUCLID:def 13
for b1, b2 being Element of REAL a1 st b1 = a2 & b2 = a3 holds
a4 = b1 - b2;
existence
ex b1 being Point of (TOP-REAL c1) st
for b2, b3 being Element of REAL c1 st b2 = c2 & b3 = c3 holds
b1 = b2 - b3
proof end;
uniqueness
for b1, b2 being Point of (TOP-REAL c1) st ( for b3, b4 being Element of REAL c1 st b3 = c2 & b4 = c3 holds
b1 = b3 - b4 ) & ( for b3, b4 being Element of REAL c1 st b3 = c2 & b4 = c3 holds
b2 = b3 - b4 ) holds
b1 = b2
proof end;
end;

:: deftheorem Def13 defines - EUCLID:def 13 :
for b1 being Nat
for b2, b3, b4 being Point of (TOP-REAL b1) holds
( b4 = b2 - b3 iff for b5, b6 being Element of REAL b1 st b5 = b2 & b6 = b3 holds
b4 = b5 - b6 );

theorem Th45: :: EUCLID:45
for b1 being Nat
for b2, b3 being Point of (TOP-REAL b1) holds b2 - b3 = b2 + (- b3)
proof end;

theorem Th46: :: EUCLID:46
for b1 being Nat
for b2 being Point of (TOP-REAL b1) holds b2 - b2 = 0.REAL b1
proof end;

theorem Th47: :: EUCLID:47
for b1 being Nat
for b2, b3 being Point of (TOP-REAL b1) st b2 - b3 = 0.REAL b1 holds
b2 = b3
proof end;

theorem Th48: :: EUCLID:48
for b1 being Nat
for b2, b3 being Point of (TOP-REAL b1) holds
( - (b2 - b3) = b3 - b2 & - (b2 - b3) = (- b2) + b3 )
proof end;

theorem Th49: :: EUCLID:49
for b1 being Nat
for b2, b3, b4 being Point of (TOP-REAL b1) holds b2 + (b3 - b4) = (b2 + b3) - b4
proof end;

theorem Th50: :: EUCLID:50
for b1 being Nat
for b2, b3, b4 being Point of (TOP-REAL b1) holds b2 - (b3 + b4) = (b2 - b3) - b4
proof end;

theorem Th51: :: EUCLID:51
for b1 being Nat
for b2, b3, b4 being Point of (TOP-REAL b1) holds b2 - (b3 - b4) = (b2 - b3) + b4
proof end;

theorem Th52: :: EUCLID:52
for b1 being Nat
for b2, b3 being Point of (TOP-REAL b1) holds
( b2 = (b2 + b3) - b3 & b2 = (b2 - b3) + b3 )
proof end;

theorem Th53: :: EUCLID:53
for b1 being Nat
for b2, b3 being Point of (TOP-REAL b1)
for b4 being real number holds b4 * (b2 - b3) = (b4 * b2) - (b4 * b3)
proof end;

theorem Th54: :: EUCLID:54
for b1 being Nat
for b2 being Point of (TOP-REAL b1)
for b3, b4 being real number holds (b3 - b4) * b2 = (b3 * b2) - (b4 * b2)
proof end;

theorem Th55: :: EUCLID:55
for b1 being Point of (TOP-REAL 2) ex b2, b3 being Real st b1 = <*b2,b3*> by FINSEQ_2:120;

definition
let c1 be Point of (TOP-REAL 2);
func c1 `1 -> Real means :Def14: :: EUCLID:def 14
for b1 being FinSequence st a1 = b1 holds
a2 = b1 . 1;
existence
ex b1 being Real st
for b2 being FinSequence st c1 = b2 holds
b1 = b2 . 1
proof end;
uniqueness
for b1, b2 being Real st ( for b3 being FinSequence st c1 = b3 holds
b1 = b3 . 1 ) & ( for b3 being FinSequence st c1 = b3 holds
b2 = b3 . 1 ) holds
b1 = b2
proof end;
func c1 `2 -> Real means :Def15: :: EUCLID:def 15
for b1 being FinSequence st a1 = b1 holds
a2 = b1 . 2;
existence
ex b1 being Real st
for b2 being FinSequence st c1 = b2 holds
b1 = b2 . 2
proof end;
uniqueness
for b1, b2 being Real st ( for b3 being FinSequence st c1 = b3 holds
b1 = b3 . 2 ) & ( for b3 being FinSequence st c1 = b3 holds
b2 = b3 . 2 ) holds
b1 = b2
proof end;
end;

:: deftheorem Def14 defines `1 EUCLID:def 14 :
for b1 being Point of (TOP-REAL 2)
for b2 being Real holds
( b2 = b1 `1 iff for b3 being FinSequence st b1 = b3 holds
b2 = b3 . 1 );

:: deftheorem Def15 defines `2 EUCLID:def 15 :
for b1 being Point of (TOP-REAL 2)
for b2 being Real holds
( b2 = b1 `2 iff for b3 being FinSequence st b1 = b3 holds
b2 = b3 . 2 );

definition
let c1, c2 be real number ;
func |[c1,c2]| -> Point of (TOP-REAL 2) equals :: EUCLID:def 16
<*a1,a2*>;
coherence
<*c1,c2*> is Point of (TOP-REAL 2)
proof end;
end;

:: deftheorem Def16 defines |[ EUCLID:def 16 :
for b1, b2 being real number holds |[b1,b2]| = <*b1,b2*>;

theorem Th56: :: EUCLID:56
for b1, b2 being real number holds
( |[b1,b2]| `1 = b1 & |[b1,b2]| `2 = b2 )
proof end;

theorem Th57: :: EUCLID:57
for b1 being Point of (TOP-REAL 2) holds b1 = |[(b1 `1 ),(b1 `2 )]|
proof end;

theorem Th58: :: EUCLID:58
0.REAL 2 = |[0,0]| by FINSEQ_2:75;

theorem Th59: :: EUCLID:59
for b1, b2 being Point of (TOP-REAL 2) holds b1 + b2 = |[((b1 `1 ) + (b2 `1 )),((b1 `2 ) + (b2 `2 ))]|
proof end;

theorem Th60: :: EUCLID:60
for b1, b2, b3, b4 being real number holds |[b1,b2]| + |[b3,b4]| = |[(b1 + b3),(b2 + b4)]|
proof end;

theorem Th61: :: EUCLID:61
for b1 being real number
for b2 being Point of (TOP-REAL 2) holds b1 * b2 = |[(b1 * (b2 `1 )),(b1 * (b2 `2 ))]|
proof end;

theorem Th62: :: EUCLID:62
for b1, b2, b3 being real number holds b1 * |[b2,b3]| = |[(b1 * b2),(b1 * b3)]|
proof end;

theorem Th63: :: EUCLID:63
for b1 being Point of (TOP-REAL 2) holds - b1 = |[(- (b1 `1 )),(- (b1 `2 ))]|
proof end;

theorem Th64: :: EUCLID:64
for b1, b2 being real number holds - |[b1,b2]| = |[(- b1),(- b2)]|
proof end;

theorem Th65: :: EUCLID:65
for b1, b2 being Point of (TOP-REAL 2) holds b1 - b2 = |[((b1 `1 ) - (b2 `1 )),((b1 `2 ) - (b2 `2 ))]|
proof end;

theorem Th66: :: EUCLID:66
for b1, b2, b3, b4 being real number holds |[b1,b2]| - |[b3,b4]| = |[(b1 - b3),(b2 - b4)]|
proof end;