I find one problem I run into when studying higher maths is that the problems that come along with them are just so difficult sometimes. I find that I spend so much time trying to figure out how to solve the problem that I lose sight of the actual material. One quarter was particularly bad, the second quarter of a graduate class on functional analysis. I really liked the class, but I feel like I got the least out of it compared to all three quarters. The teacher loved clever problems, and it took me easily 20-30 hours a week to do the homework and at the end I had no idea what I had done. I just threw every theorem I had at it. At the end of proving some obscure technical result about weak-* convergence, I would have totally forgot what weak-* convergence even meant. The problem, while seriously stretching my problem solving skills, did nothing to help me understand weak-* convergence. Not blaming the teacher, it was a fun class, I just wish I understood the topics better. Anyway, I'm looking for books that have easy, straightforward problems in graduate subjects to cement the foundations. Something with true/false questions or simple computations/proofs that follow directly from the definition. Doesn't have to be functional analysis, it could be measure/probability theory, algebraic topology, differential geometry, etc.