I've always loved the theorem-proof format in textbooks, e.g. Hardy and Wright's Introduction to the theory of numbers. However, the problem is that I can't remember anything I read in this format because usually books of this kind don't have exercises at the end (not all, but usually). What do you think is the best way to actually learn from theorem-proof type books? Should I read a section, write down all the theorems and then close the book and try proving them myself a week later or so? Should I just take notes as I read and construct my own problems to practise with as I go along?