what are your opinions on schaum's outlines? is it meant as a supplementary guide for students who are struggling? or is it good for students of all skill levels? i noticed that many of the problems (in math) are just asking you to prove theorems already found in textbooks. on the other hand, it also has some good exercises with solutions, that would typically be found in tests. the books only cover courses up to 2nd year only. why doesn't it have titles for 3rd year and 4th year level courses?