Nit: I'm not sure I would consider Cantor Diagonalization non-constructive. I wouldn't consider it constructive either, though. It's used to prove things like t

Nit: I'm not sure I would consider Cantor Diagonalization non-constructive. I wouldn't consider it constructive either, though. It's used to prove things like the uncountability of the reals: how do you constructively prove that no bijection exists between the naturals and the reals?