Surveys the theorems, structures and proofs underpinning much of mathematics. Keep in mind that while comprehensive, it is not exhaustive. It presumes a great deal of maturity and a willingness to pause and explore a concept, often with other texts. The section on Hilbert Spaces, for instance, could be and has been dealt with in books of several hundred pages.
The exercises range from tricky to exceedingly challenging for anybody but the truly gifted, and a single solution could fill an entire tutorial.