I'll add that this book is well above normal high school math. It was our summer reading for Math Olympiad training. I narrowly missed a place on the Australia

I'll add that this book is well above normal high school math. It was our summer reading for Math Olympiad training. I narrowly missed a place on the Australian IMO team, and at the time was annoyed at myself for being beaten by a 10 year old. He, of course, was Terry Tao, youngest ever winner of a IMO medal, and a Fields Medalist a few years later.