let f be PartFunc of REAL,COMPLEX; :: thesis: for A being non empty closed_interval Subset of REAL
for a, b being Real st A = [.b,a.] holds
- (integral (f,A)) = integral (f,a,b)

let A be non empty closed_interval Subset of REAL; :: thesis: for a, b being Real st A = [.b,a.] holds
- (integral (f,A)) = integral (f,a,b)

let a, b be Real; :: thesis: ( A = [.b,a.] implies - (integral (f,A)) = integral (f,a,b) )
assume A1: A = [.b,a.] ; :: thesis: - (integral (f,A)) = integral (f,a,b)
A2: ( Re (integral (f,a,b)) = integral ((Re f),a,b) & Im (integral (f,a,b)) = integral ((Im f),a,b) ) by COMPLEX1:12;
A3: Re (- (integral (f,A))) = - (Re (integral (f,A))) by COMPLEX1:17
.= - (integral ((Re f),A)) by COMPLEX1:12 ;
A4: Im (- (integral (f,A))) = - (Im (integral (f,A))) by COMPLEX1:17
.= - (integral ((Im f),A)) by COMPLEX1:12 ;
A5: Re (- (integral (f,A))) = Re (integral (f,a,b)) by ;
Im (- (integral (f,A))) = Im (integral (f,a,b)) by ;
hence - (integral (f,A)) = integral (f,a,b) by A5; :: thesis: verum