let X be non empty set ; :: thesis:
let S be SigmaField of X; :: thesis:
let M be sigma_Measure of S; :: thesis:
let E be Element of S; :: thesis:
let f be nonpositive PartFunc of X,ExtREAL; :: thesis:
assume ex A being Element of S st
( A = dom f & f is A -measurable ) ; :: thesis:
then consider A being Element of S such that
A2: ( A = dom f & f is A -measurable ) ;
A3: dom (max+ f) = A by A2, MESFUNC2:def 2;
A4: f = - (max- f) by Th32;
then A5: - f = max- f by Th36;
for x being Element of X st x in dom (max+ f) holds
(max+ f) . x = 0

proof

let x be Element of X; :: thesis:
assume x in dom (max+ f) ; :: thesis:
then f . x = - ((max- f) . x) by A2, A3, A4, MESFUNC1:def 7;
then - (f . x) = (max- f) . x ;
hence (max+ f) . x = 0 by MESFUNC2:21; :: thesis:

end;

then A6: integral+ (M,(max+ f)) = 0 by A3, A2, MESFUNC2:25, MESFUNC5:87;
A7: Integral (M,f) = (integral+ (M,(max+ f))) - (integral+ (M,(max- f))) by MESFUNC5:def 16
.= (integral+ (M,(max+ f))) + (- (integral+ (M,(max- f)))) by XXREAL_3:def 4 ;
hence Integral (M,f) = - (integral+ (M,(max- f))) by A6, XXREAL_3:4; :: thesis:
thus A8: Integral (M,f) = - (integral+ (M,(- f))) by A5, A7, A6, XXREAL_3:4; :: thesis:
A = dom (- f) by A2, MESFUNC1:def 7;
hence Integral (M,f) = - (Integral (M,(- f))) by A8, A2, MEASUR11:63, MESFUNC5:88; :: thesis: