A good start for real math
This books is perhaps the best gateway to real mathematics out there. It is the only introductory textbook that builds on axioms and fundamental counting up to calculus. I would like to advise the buyer that this is not really an introductory book, however. Rather, it takes what you know, and shows you how it should have been taught. Not recommended for people who are not intererested in number theory and rigirous proofs.