Are you a math student who has really shitty fundamentals and gaps in knowledge? Then I highly recommend picking up Book of Proof. The writing style and pacing assumes you've been through the rigamaroo of uni math, but you will reinforce and solidify the fundamentals of sets, logic and proof writing. I highly recommend it. It's also free: https://www.people.vcu.edu/~rhammack/BookOfProof/