> but except in mathematics we are never building on first principles In practice, mathematicians also assume "that problems we don't deal with directly are t

> but except in mathematics we are never building on first principles In practice, mathematicians also assume "that problems we don't deal with directly are taken care of by somebody else in good faith". We use theorems that others proved, and we trust that the authors and the reviewers did their job, without inspecting the proofs ourselves. Sometimes mistakes slip through, but they are usually caught fairly quickly, and can be fixed locally. In other words, we are less strict than we like to think we are, but we get away with it perfectly well.