I'm very much enjoying this book. It's been recomended to me before; I don't know why I didn't pick it up sooner.

As I read, I'm playing a game where I reconstitute coursework I had taken in college, high school, or independent studies later in life. The obvious touchpoints are things like Euclid's postulates, Reimann integrals, or epsilon/delta proofs. Newer (to me) ideas are König's lemmas or the recursive comprehension axiom. But even in these less familiar areas, Stillwell presents the concepts in such a way that I recognize that they were around before, lurking in coursework I didn't pay attention to or missed out on.