Am I the only one who’s noticed an amusing (or perhaps alarming) tendency of proofs by contradiction to sneak in places they don’t really belong?
Let me illustrate with an absurd example.
Prop 0. It is cold outside. Proof. Assume for contradiction that it is warm outside. Then it must not be snowing right now. But it is snowing right now. This is a contradiction, so our assumption was false. So it is cold outside.