Let f: A -> B and X be subsets of A.
Prove: X is a subset of f inverse of f(X)
Let b be in f(X) which implies b=f(a) where a is in X
f inverse of b=f inverse of f(a)=a which implies f inverse of b is in X
which implies X is a subset of f inverse of f(X)
qed
Did I do this correctly?
Thanks!