theorem Th65: :: MESFUN12:65

for X1, X2 being non empty set
for S1 being SigmaField of X1
for S2 being SigmaField of X2
for M2 being sigma_Measure of S2
for E being Element of sigma (measurable_rectangles (S1,S2)) st M2 is sigma_finite holds
Y-vol (E,M2) = Integral2 (M2,(chi (E,[:X1,X2:])))