TITLE: Prove that $4$ is the only solution to $2+2$.
QUESTION [11 upvotes]: This question was featured on Saturday Morning Breakfast Cereal and I haven't been able to find a proof. Can anyone help?

REPLY [3 votes]: The cartoon is a joke which doesn't bear too much analysis. The "mathematician parent" is the cartoonist's parody of such a parent. A real mathematician would not ask for a proof that the "solution is unique" in the case of addition of two specific integers, because such a request would make little sense. If we must credit the request with some sense, then perhaps an appropriate response would be at the level of "because addition is unique, Stupid!".