I am self-studying MA, I've learned elementary Calculus ( without vector calculus & Partial Differentiation) I've learned a bit of LA before. I am using these text books: 1. introduction to Analysis (so far there is no difficulty) 2. Principles of Mathematical Analysis (this one is more difficult, and often I got stuck.) So basically, my question is: 1. What am I supposed to learn before reading Principles of Mathematical Analysis ( so that I can read it more easily) or it is natural that to learn it with some hard time? Thanks!!