theorem Th50: :: RPR_1:50

for E being non empty finite set
for A, B1, B2 being Event of E st 0 < prob B1 & 0 < prob B2 & B1 \/ B2 = E & B1 misses B2 holds
prob A = ((prob (A,B1)) * (prob B1)) + ((prob (A,B2)) * (prob B2))