functions - Proof Regarding an iff Statement

Let $f:X \to Y$ be a function.

Then $f$ is one-to-one iff for all subsets $A$ and $B$ of $X$, $f(A\cap B) = f(A) \cap f(B)$.

Any proofs or guidance would be greatly appreciated

Answer

An incomplete proof of the --> part of the biconditional