I finished learning “How to Prove It: A Structured Approach, 2nd Edition” by Daniel J. Velleman a while ago.
It taught me propositional logic and first order logic for proof techniques. I was taught how to solve basic math problems. However, I didn't feel that I learned enough formal logic.
I'm learning an approach to AI based on language/semiotics and turing ordinals, and I have a feeling that formal logic might be important, but I'm not sure.
If there is particularly not a useful math field for that approach, I plan to learn linear algebra, calculus, probability, and statistics in order because those fields are necessary for computer science, machine learning, and many other disciplines. I'm not sure about discrete mathematics, yet.