:: PROB_1 semantic presentation

Lemma1: for b1, b2 being real number st 0 <= b1 holds
b2 - b1 <= b2
by XREAL_1:45;

theorem Th1: :: PROB_1:1
canceled;

theorem Th2: :: PROB_1:2
canceled;

theorem Th3: :: PROB_1:3
for b1 being real number
for b2 being Real_Sequence st ex b3 being Nat st
for b4 being Nat st b3 <= b4 holds
b2 . b4 = b1 holds
( b2 is convergent & lim b2 = b1 )
proof end;

definition
let c1 be set ;
let c2 be Subset-Family of c1;
attr a2 is compl-closed means :Def1: :: PROB_1:def 1
for b1 being Subset of a1 st b1 in a2 holds
b1 ` in a2;
end;

:: deftheorem Def1 defines compl-closed PROB_1:def 1 :
for b1 being set
for b2 being Subset-Family of b1 holds
( b2 is compl-closed iff for b3 being Subset of b1 st b3 in b2 holds
b3 ` in b2 );

registration
let c1 be set ;
cluster non empty cap-closed compl-closed Element of bool (bool a1);
existence
ex b1 being Subset-Family of c1 st
( not b1 is empty & b1 is compl-closed & b1 is cap-closed )
proof end;
end;

definition
let c1 be set ;
mode Field_Subset of a1 is non empty cap-closed compl-closed Subset-Family of a1;
end;

theorem Th4: :: PROB_1:4
for b1 being set
for b2, b3 being Subset of b1 holds {b2,b3} is Subset-Family of b1
proof end;

theorem Th5: :: PROB_1:5
canceled;

theorem Th6: :: PROB_1:6
for b1 being set
for b2 being Field_Subset of b1 ex b3 being Subset of b1 st b3 in b2
proof end;

theorem Th7: :: PROB_1:7
canceled;

theorem Th8: :: PROB_1:8
canceled;

theorem Th9: :: PROB_1:9
for b1 being set
for b2 being Field_Subset of b1
for b3, b4 being set st b3 in b2 & b4 in b2 holds
b3 \/ b4 in b2
proof end;

theorem Th10: :: PROB_1:10
for b1 being set
for b2 being Field_Subset of b1 holds {} in b2
proof end;

theorem Th11: :: PROB_1:11
for b1 being set
for b2 being Field_Subset of b1 holds b1 in b2
proof end;

theorem Th12: :: PROB_1:12
for b1 being set
for b2 being Field_Subset of b1
for b3, b4 being Subset of b1 st b3 in b2 & b4 in b2 holds
b3 \ b4 in b2
proof end;

theorem Th13: :: PROB_1:13
for b1 being set
for b2 being Field_Subset of b1
for b3, b4 being set holds
( b3 \ b4 misses b4 & ( b3 in b2 & b4 in b2 implies (b3 \ b4) \/ b4 in b2 ) )
proof end;

theorem Th14: :: PROB_1:14
for b1 being set holds {{} ,b1} is Field_Subset of b1
proof end;

theorem Th15: :: PROB_1:15
for b1 being set holds bool b1 is Field_Subset of b1
proof end;

theorem Th16: :: PROB_1:16
for b1 being set
for b2 being Field_Subset of b1 holds
( {{} ,b1} c= b2 & b2 c= bool b1 )
proof end;

theorem Th17: :: PROB_1:17
canceled;

theorem Th18: :: PROB_1:18
for b1 being set holds
( ( for b2 being set st b2 in [:NAT ,{b1}:] holds
ex b3, b4 being set st [b3,b4] = b2 ) & ( for b2, b3, b4 being set st [b2,b3] in [:NAT ,{b1}:] & [b2,b4] in [:NAT ,{b1}:] holds
b3 = b4 ) )
proof end;

theorem Th19: :: PROB_1:19
for b1 being set ex b2 being Function st
( dom b2 = NAT & ( for b3 being Nat holds b2 . b3 = b1 ) )
proof end;

definition
let c1 be set ;
mode SetSequence of a1 is Function of NAT , bool a1;
end;

Lemma11: for b1 being set
for b2 being SetSequence of b1 holds
( dom b2 = NAT & ( for b3 being Nat holds b2 . b3 in bool b1 ) )
by FUNCT_2:def 1;

theorem Th20: :: PROB_1:20
canceled;

theorem Th21: :: PROB_1:21
for b1 being set ex b2 being SetSequence of b1 st
for b3 being Nat holds b2 . b3 = b1
proof end;

theorem Th22: :: PROB_1:22
for b1 being set
for b2, b3 being Subset of b1 ex b4 being SetSequence of b1 st
( b4 . 0 = b2 & ( for b5 being Nat st b5 <> 0 holds
b4 . b5 = b3 ) )
proof end;

definition
let c1 be set ;
let c2 be SetSequence of c1;
let c3 be Nat;
redefine func . as c2 . c3 -> Subset of a1;
coherence
c2 . c3 is Subset of c1
by Lemma11;
end;

theorem Th23: :: PROB_1:23
for b1 being set
for b2 being SetSequence of b1 holds union (rng b2) is Subset of b1
proof end;

definition
let c1 be set ;
let c2 be SetSequence of c1;
redefine func Union as Union c2 -> Subset of a1;
coherence
Union c2 is Subset of c1
proof end;
end;

theorem Th24: :: PROB_1:24
canceled;

theorem Th25: :: PROB_1:25
for b1, b2 being set
for b3 being SetSequence of b1 holds
( b2 in Union b3 iff ex b4 being Nat st b2 in b3 . b4 )
proof end;

theorem Th26: :: PROB_1:26
for b1 being set
for b2 being SetSequence of b1 ex b3 being SetSequence of b1 st
for b4 being Nat holds b3 . b4 = (b2 . b4) `
proof end;

definition
let c1 be set ;
let c2 be SetSequence of c1;
canceled;
canceled;
func Complement c2 -> SetSequence of a1 means :Def4: :: PROB_1:def 4
for b1 being Nat holds a3 . b1 = (a2 . b1) ` ;
existence
ex b1 being SetSequence of c1 st
for b2 being Nat holds b1 . b2 = (c2 . b2) `
by Th26;
uniqueness
for b1, b2 being SetSequence of c1 st ( for b3 being Nat holds b1 . b3 = (c2 . b3) ` ) & ( for b3 being Nat holds b2 . b3 = (c2 . b3) ` ) holds
b1 = b2
proof end;
involutiveness
for b1, b2 being SetSequence of c1 st ( for b3 being Nat holds b1 . b3 = (b2 . b3) ` ) holds
for b3 being Nat holds b2 . b3 = (b1 . b3) `
proof end;
end;

:: deftheorem Def2 PROB_1:def 2 :
canceled;

:: deftheorem Def3 PROB_1:def 3 :
canceled;

:: deftheorem Def4 defines Complement PROB_1:def 4 :
for b1 being set
for b2, b3 being SetSequence of b1 holds
( b3 = Complement b2 iff for b4 being Nat holds b3 . b4 = (b2 . b4) ` );

definition
let c1 be set ;
let c2 be SetSequence of c1;
func Intersection c2 -> Subset of a1 equals :: PROB_1:def 5
(Union (Complement a2)) ` ;
correctness
coherence
(Union (Complement c2)) ` is Subset of c1
;
;
end;

:: deftheorem Def5 defines Intersection PROB_1:def 5 :
for b1 being set
for b2 being SetSequence of b1 holds Intersection b2 = (Union (Complement b2)) ` ;

theorem Th27: :: PROB_1:27
canceled;

theorem Th28: :: PROB_1:28
canceled;

theorem Th29: :: PROB_1:29
for b1, b2 being set
for b3 being SetSequence of b1 holds
( b2 in Intersection b3 iff for b4 being Nat holds b2 in b3 . b4 )
proof end;

theorem Th30: :: PROB_1:30
for b1 being set
for b2 being SetSequence of b1
for b3, b4 being Subset of b1 st b2 . 0 = b3 & ( for b5 being Nat st b5 <> 0 holds
b2 . b5 = b4 ) holds
Intersection b2 = b3 /\ b4
proof end;

definition
let c1 be set ;
let c2 be SetSequence of c1;
attr a2 is non-increasing means :Def6: :: PROB_1:def 6
for b1, b2 being Nat st b1 <= b2 holds
a2 . b2 c= a2 . b1;
attr a2 is non-decreasing means :: PROB_1:def 7
for b1, b2 being Nat st b1 <= b2 holds
a2 . b1 c= a2 . b2;
end;

:: deftheorem Def6 defines non-increasing PROB_1:def 6 :
for b1 being set
for b2 being SetSequence of b1 holds
( b2 is non-increasing iff for b3, b4 being Nat st b3 <= b4 holds
b2 . b4 c= b2 . b3 );

:: deftheorem Def7 defines non-decreasing PROB_1:def 7 :
for b1 being set
for b2 being SetSequence of b1 holds
( b2 is non-decreasing iff for b3, b4 being Nat st b3 <= b4 holds
b2 . b3 c= b2 . b4 );

definition
let c1 be set ;
mode SigmaField of c1 -> non empty Subset-Family of a1 means :Def8: :: PROB_1:def 8
( ( for b1 being SetSequence of a1 st ( for b2 being Nat holds b1 . b2 in a2 ) holds
Intersection b1 in a2 ) & ( for b1 being Subset of a1 st b1 in a2 holds
b1 ` in a2 ) );
existence
ex b1 being non empty Subset-Family of c1 st
( ( for b2 being SetSequence of c1 st ( for b3 being Nat holds b2 . b3 in b1 ) holds
Intersection b2 in b1 ) & ( for b2 being Subset of c1 st b2 in b1 holds
b2 ` in b1 ) )
proof end;
end;

:: deftheorem Def8 defines SigmaField PROB_1:def 8 :
for b1 being set
for b2 being non empty Subset-Family of b1 holds
( b2 is SigmaField of b1 iff ( ( for b3 being SetSequence of b1 st ( for b4 being Nat holds b3 . b4 in b2 ) holds
Intersection b3 in b2 ) & ( for b3 being Subset of b1 st b3 in b2 holds
b3 ` in b2 ) ) );

theorem Th31: :: PROB_1:31
canceled;

theorem Th32: :: PROB_1:32
for b1 being set
for b2 being non empty set holds
( b2 is SigmaField of b1 iff ( b2 c= bool b1 & ( for b3 being SetSequence of b1 st ( for b4 being Nat holds b3 . b4 in b2 ) holds
Intersection b3 in b2 ) & ( for b3 being Subset of b1 st b3 in b2 holds
b3 ` in b2 ) ) ) by Def8;

theorem Th33: :: PROB_1:33
canceled;

theorem Th34: :: PROB_1:34
canceled;

theorem Th35: :: PROB_1:35
for b1, b2 being set st b1 is SigmaField of b2 holds
b1 is Field_Subset of b2
proof end;

registration
let c1 be set ;
cluster -> cap-closed compl-closed SigmaField of a1;
coherence
for b1 being SigmaField of c1 holds
( b1 is cap-closed & b1 is compl-closed )
by Th35;
end;

theorem Th36: :: PROB_1:36
canceled;

theorem Th37: :: PROB_1:37
canceled;

theorem Th38: :: PROB_1:38
for b1 being set
for b2 being SigmaField of b1 ex b3 being Subset of b1 st b3 in b2
proof end;

theorem Th39: :: PROB_1:39
canceled;

theorem Th40: :: PROB_1:40
canceled;

theorem Th41: :: PROB_1:41
for b1 being set
for b2 being SigmaField of b1
for b3, b4 being Subset of b1 st b3 in b2 & b4 in b2 holds
b3 \/ b4 in b2 by Th9;

theorem Th42: :: PROB_1:42
for b1 being set
for b2 being SigmaField of b1 holds {} in b2 by Th10;

theorem Th43: :: PROB_1:43
for b1 being set
for b2 being SigmaField of b1 holds b1 in b2 by Th11;

theorem Th44: :: PROB_1:44
for b1 being set
for b2 being SigmaField of b1
for b3, b4 being Subset of b1 st b3 in b2 & b4 in b2 holds
b3 \ b4 in b2 by Th12;

definition
let c1 be set ;
let c2 be SigmaField of c1;
mode SetSequence of c2 -> SetSequence of a1 means :Def9: :: PROB_1:def 9
for b1 being Nat holds a3 . b1 in a2;
existence
ex b1 being SetSequence of c1 st
for b2 being Nat holds b1 . b2 in c2
proof end;
end;

:: deftheorem Def9 defines SetSequence PROB_1:def 9 :
for b1 being set
for b2 being SigmaField of b1
for b3 being SetSequence of b1 holds
( b3 is SetSequence of b2 iff for b4 being Nat holds b3 . b4 in b2 );

theorem Th45: :: PROB_1:45
canceled;

theorem Th46: :: PROB_1:46
for b1 being set
for b2 being SigmaField of b1
for b3 being SetSequence of b2 holds Union b3 in b2
proof end;

definition
let c1 be set ;
let c2 be SigmaField of c1;
mode Event of c2 -> Subset of a1 means :Def10: :: PROB_1:def 10
a3 in a2;
existence
ex b1 being Subset of c1 st b1 in c2
proof end;
end;

:: deftheorem Def10 defines Event PROB_1:def 10 :
for b1 being set
for b2 being SigmaField of b1
for b3 being Subset of b1 holds
( b3 is Event of b2 iff b3 in b2 );

theorem Th47: :: PROB_1:47
canceled;

theorem Th48: :: PROB_1:48
for b1, b2 being set
for b3 being SigmaField of b1 st b2 in b3 holds
b2 is Event of b3 by Def10;

theorem Th49: :: PROB_1:49
for b1 being set
for b2 being SigmaField of b1
for b3, b4 being Event of b2 holds b3 /\ b4 is Event of b2
proof end;

theorem Th50: :: PROB_1:50
for b1 being set
for b2 being SigmaField of b1
for b3 being Event of b2 holds b3 ` is Event of b2
proof end;

theorem Th51: :: PROB_1:51
for b1 being set
for b2 being SigmaField of b1
for b3, b4 being Event of b2 holds b3 \/ b4 is Event of b2
proof end;

theorem Th52: :: PROB_1:52
for b1 being set
for b2 being SigmaField of b1 holds {} is Event of b2
proof end;

theorem Th53: :: PROB_1:53
for b1 being set
for b2 being SigmaField of b1 holds b1 is Event of b2
proof end;

theorem Th54: :: PROB_1:54
for b1 being set
for b2 being SigmaField of b1
for b3, b4 being Event of b2 holds b3 \ b4 is Event of b2
proof end;

registration
let c1 be set ;
let c2 be SigmaField of c1;
cluster empty Event of a2;
existence
ex b1 being Event of c2 st b1 is empty
proof end;
end;

definition
let c1 be set ;
let c2 be SigmaField of c1;
func [#] c2 -> Event of a2 equals :: PROB_1:def 11
a1;
coherence
c1 is Event of c2
by Th53;
end;

:: deftheorem Def11 defines [#] PROB_1:def 11 :
for b1 being set
for b2 being SigmaField of b1 holds [#] b2 = b1;

definition
let c1 be set ;
let c2 be SigmaField of c1;
let c3, c4 be Event of c2;
redefine func /\ as c3 /\ c4 -> Event of a2;
coherence
c3 /\ c4 is Event of c2
by Th49;
redefine func \/ as c3 \/ c4 -> Event of a2;
coherence
c3 \/ c4 is Event of c2
by Th51;
redefine func \ as c3 \ c4 -> Event of a2;
coherence
c3 \ c4 is Event of c2
by Th54;
end;

theorem Th55: :: PROB_1:55
canceled;

theorem Th56: :: PROB_1:56
canceled;

theorem Th57: :: PROB_1:57
for b1 being non empty set
for b2 being SetSequence of b1
for b3 being SigmaField of b1 holds
( b2 is SetSequence of b3 iff for b4 being Nat holds b2 . b4 is Event of b3 )
proof end;

theorem Th58: :: PROB_1:58
for b1 being non empty set
for b2 being SetSequence of b1
for b3 being SigmaField of b1 st b2 is SetSequence of b3 holds
Union b2 is Event of b3
proof end;

theorem Th59: :: PROB_1:59
for b1 being non empty set
for b2 being set
for b3 being SigmaField of b1 ex b4 being Function st
( dom b4 = b3 & ( for b5 being Subset of b1 st b5 in b3 holds
( ( b2 in b5 implies b4 . b5 = 1 ) & ( not b2 in b5 implies b4 . b5 = 0 ) ) ) )
proof end;

theorem Th60: :: PROB_1:60
for b1 being non empty set
for b2 being set
for b3 being SigmaField of b1 ex b4 being Function of b3, REAL st
for b5 being Subset of b1 st b5 in b3 holds
( ( b2 in b5 implies b4 . b5 = 1 ) & ( not b2 in b5 implies b4 . b5 = 0 ) )
proof end;

theorem Th61: :: PROB_1:61
canceled;

theorem Th62: :: PROB_1:62
for b1 being non empty set
for b2 being SigmaField of b1
for b3 being SetSequence of b2
for b4 being Function of b2, REAL holds b4 * b3 is Real_Sequence
proof end;

definition
let c1 be non empty set ;
let c2 be SigmaField of c1;
let c3 be SetSequence of c2;
let c4 be Function of c2, REAL ;
redefine func * as c4 * c3 -> Real_Sequence;
coherence
c3 * c4 is Real_Sequence
by Th62;
end;

definition
let c1 be non empty set ;
let c2 be SigmaField of c1;
let c3 be Function of c2, REAL ;
let c4 be Event of c2;
redefine func . as c3 . c4 -> Real;
coherence
c3 . c4 is Real
proof end;
end;

definition
let c1 be non empty set ;
let c2 be SigmaField of c1;
canceled;
mode Probability of c2 -> Function of a2, REAL means :Def13: :: PROB_1:def 13
( ( for b1 being Event of a2 holds 0 <= a3 . b1 ) & a3 . a1 = 1 & ( for b1, b2 being Event of a2 st b1 misses b2 holds
a3 . (b1 \/ b2) = (a3 . b1) + (a3 . b2) ) & ( for b1 being SetSequence of a2 st b1 is non-increasing holds
( a3 * b1 is convergent & lim (a3 * b1) = a3 . (Intersection b1) ) ) );
existence
ex b1 being Function of c2, REAL st
( ( for b2 being Event of c2 holds 0 <= b1 . b2 ) & b1 . c1 = 1 & ( for b2, b3 being Event of c2 st b2 misses b3 holds
b1 . (b2 \/ b3) = (b1 . b2) + (b1 . b3) ) & ( for b2 being SetSequence of c2 st b2 is non-increasing holds
( b1 * b2 is convergent & lim (b1 * b2) = b1 . (Intersection b2) ) ) )
proof end;
end;

:: deftheorem Def12 PROB_1:def 12 :
canceled;

:: deftheorem Def13 defines Probability PROB_1:def 13 :
for b1 being non empty set
for b2 being SigmaField of b1
for b3 being Function of b2, REAL holds
( b3 is Probability of b2 iff ( ( for b4 being Event of b2 holds 0 <= b3 . b4 ) & b3 . b1 = 1 & ( for b4, b5 being Event of b2 st b4 misses b5 holds
b3 . (b4 \/ b5) = (b3 . b4) + (b3 . b5) ) & ( for b4 being SetSequence of b2 st b4 is non-increasing holds
( b3 * b4 is convergent & lim (b3 * b4) = b3 . (Intersection b4) ) ) ) );

theorem Th63: :: PROB_1:63
canceled;

theorem Th64: :: PROB_1:64
for b1 being non empty set
for b2 being SigmaField of b1
for b3 being Probability of b2 holds b3 . {} = 0
proof end;

theorem Th65: :: PROB_1:65
canceled;

theorem Th66: :: PROB_1:66
for b1 being non empty set
for b2 being SigmaField of b1
for b3 being Probability of b2 holds b3 . ([#] b2) = 1 by Def13;

theorem Th67: :: PROB_1:67
for b1 being non empty set
for b2 being SigmaField of b1
for b3 being Event of b2
for b4 being Probability of b2 holds (b4 . (([#] b2) \ b3)) + (b4 . b3) = 1
proof end;

theorem Th68: :: PROB_1:68
for b1 being non empty set
for b2 being SigmaField of b1
for b3 being Event of b2
for b4 being Probability of b2 holds b4 . (([#] b2) \ b3) = 1 - (b4 . b3)
proof end;

theorem Th69: :: PROB_1:69
for b1 being non empty set
for b2 being SigmaField of b1
for b3, b4 being Event of b2
for b5 being Probability of b2 st b3 c= b4 holds
b5 . (b4 \ b3) = (b5 . b4) - (b5 . b3)
proof end;

theorem Th70: :: PROB_1:70
for b1 being non empty set
for b2 being SigmaField of b1
for b3, b4 being Event of b2
for b5 being Probability of b2 st b3 c= b4 holds
b5 . b3 <= b5 . b4
proof end;

theorem Th71: :: PROB_1:71
for b1 being non empty set
for b2 being SigmaField of b1
for b3 being Event of b2
for b4 being Probability of b2 holds b4 . b3 <= 1
proof end;

theorem Th72: :: PROB_1:72
for b1 being non empty set
for b2 being SigmaField of b1
for b3, b4 being Event of b2
for b5 being Probability of b2 holds b5 . (b3 \/ b4) = (b5 . b3) + (b5 . (b4 \ b3))
proof end;

theorem Th73: :: PROB_1:73
for b1 being non empty set
for b2 being SigmaField of b1
for b3, b4 being Event of b2
for b5 being Probability of b2 holds b5 . (b3 \/ b4) = (b5 . b3) + (b5 . (b4 \ (b3 /\ b4)))
proof end;

theorem Th74: :: PROB_1:74
for b1 being non empty set
for b2 being SigmaField of b1
for b3, b4 being Event of b2
for b5 being Probability of b2 holds b5 . (b3 \/ b4) = ((b5 . b3) + (b5 . b4)) - (b5 . (b3 /\ b4))
proof end;

theorem Th75: :: PROB_1:75
for b1 being non empty set
for b2 being SigmaField of b1
for b3, b4 being Event of b2
for b5 being Probability of b2 holds b5 . (b3 \/ b4) <= (b5 . b3) + (b5 . b4)
proof end;

theorem Th76: :: PROB_1:76
for b1 being non empty set holds bool b1 is SigmaField of b1
proof end;

Lemma43: for b1 being non empty set
for b2 being Subset-Family of b1 ex b3 being SigmaField of b1 st
( b2 c= b3 & ( for b4 being set st b2 c= b4 & b4 is SigmaField of b1 holds
b3 c= b4 ) )
proof end;

definition
let c1 be non empty set ;
let c2 be Subset-Family of c1;
func sigma c2 -> SigmaField of a1 means :: PROB_1:def 14
( a2 c= a3 & ( for b1 being set st a2 c= b1 & b1 is SigmaField of a1 holds
a3 c= b1 ) );
existence
ex b1 being SigmaField of c1 st
( c2 c= b1 & ( for b2 being set st c2 c= b2 & b2 is SigmaField of c1 holds
b1 c= b2 ) )
by Lemma43;
uniqueness
for b1, b2 being SigmaField of c1 st c2 c= b1 & ( for b3 being set st c2 c= b3 & b3 is SigmaField of c1 holds
b1 c= b3 ) & c2 c= b2 & ( for b3 being set st c2 c= b3 & b3 is SigmaField of c1 holds
b2 c= b3 ) holds
b1 = b2
proof end;
end;

:: deftheorem Def14 defines sigma PROB_1:def 14 :
for b1 being non empty set
for b2 being Subset-Family of b1
for b3 being SigmaField of b1 holds
( b3 = sigma b2 iff ( b2 c= b3 & ( for b4 being set st b2 c= b4 & b4 is SigmaField of b1 holds
b3 c= b4 ) ) );

definition
let c1 be real number ;
func halfline c1 -> Subset of REAL equals :: PROB_1:def 15
{ b1 where B is Element of REAL : b1 < a1 } ;
coherence
{ b1 where B is Element of REAL : b1 < c1 } is Subset of REAL
proof end;
end;

:: deftheorem Def15 defines halfline PROB_1:def 15 :
for b1 being real number holds halfline b1 = { b2 where B is Element of REAL : b2 < b1 } ;

definition
func Family_of_halflines -> Subset-Family of REAL equals :: PROB_1:def 16
{ b1 where B is Subset of REAL : ex b1 being real number st b1 = halfline b2 } ;
coherence
{ b1 where B is Subset of REAL : ex b1 being real number st b1 = halfline b2 } is Subset-Family of REAL
proof end;
end;

:: deftheorem Def16 defines Family_of_halflines PROB_1:def 16 :
Family_of_halflines = { b1 where B is Subset of REAL : ex b1 being real number st b1 = halfline b2 } ;

definition
func Borel_Sets -> SigmaField of REAL equals :: PROB_1:def 17
sigma Family_of_halflines ;
correctness
coherence
sigma Family_of_halflines is SigmaField of REAL
;
;
end;

:: deftheorem Def17 defines Borel_Sets PROB_1:def 17 :
Borel_Sets = sigma Family_of_halflines ;