theorem Th20: :: MEASUR11:26

for X, Y being non empty set
for E1, E2 being Subset of [:X,Y:]
for p being set holds
( X-section ((E1 \/ E2),p) = (X-section (E1,p)) \/ (X-section (E2,p)) & Y-section ((E1 \/ E2),p) = (Y-section (E1,p)) \/ (Y-section (E2,p)) )