Let f:A->B, where A and B are nonempty

Question

Prove that f(S1 - f(S2) is a proper subset of f(S1 -S2) fo all subsets S1 and S2 of A.

Give an example where there are subsets S1 and S2 of A such that
f(S1) - f(S2) does not equal f(S1-S2)