theorem Th2: :: MEASUR11:8

for X1, X2 being non empty set
for S1 being SigmaField of X1
for S2 being SigmaField of X2
for M1 being sigma_Measure of S1
for M2 being sigma_Measure of S2 holds product_sigma_Measure (M1,M2) is sigma_Measure of (sigma (measurable_rectangles (S1,S2)))