Where did you all learn proofs from?
So, I am finally starting to learn proofs in my MATH 134 class at the UWashington, but it's awfully late compared to some of you. Still though, most math competitions up to the level of the AIME don't use proofs. You don't learn them from school. It's my speculation, but I doubt that most people would check out a book from the library specifically to learn about them. So, where did you gain that knowledge?