Need a possible proof for $A\cap B=A\cup B$ I need to prove that-
If $A,B\subseteq U$ where $U$ is the universal set, then $A\cap B=A\cup B$.
I've been thinking a lot about it and I don;t think it's possible. Yet, I would like to confirm it for a possible proof.
What I think is that $A$ and $B$ can be mutually exclussive and thus $A\cup B$ will be something while $A\cap B$ would be a null set.

This is not true. Take $U=\{1,2,3\}$, $A=\{1\}$ and $B=\{2\}$ for a counterexample.
