[To Be Turned in on Wednesday]
- Let $f\colon X\to Y$ be a function.
- Show that $f(f^{-1}(B))\subseteq B$ for all subsets $B$ of $Y$.
- Give an example of a function $f$ and a set $B$ that shows that the subset need not be an equality.
- What condition on $f$ would guarantee equality? (Prove that you are right).
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