Some things remain as well. Such as references to where you learned the thing, the ability to pattern match (Oh this is a problem of form X, which is listed in

Some things remain as well. Such as references to where you learned the thing, the ability to pattern match (Oh this is a problem of form X, which is listed in textbooks A,B and C. I don't remember how to solve it, but I used to. Therefore given that I know I'm capable of solving it, as I've done it before, I know the problem type, and I know where to study it, I'm confident to tell you I can solve it in two weeks."