Examples 7.3.10(a): Properties of Measure
For any sets A and B we have:(A B) (A comp(B)) = Aand A B and A comp(B) are disjoint. Therefore, by additivity of measure we have:
m(A B) + m(A comp(B)) = m(A)Therefore
m(A - B) = m(A) - m(A B)as we had to prove. If B A then A B = B so that
m(A - B) = m(A) - m(B)