MIT has a very useful course that covers the (often overlooked) basics of discrete math that
show up all over computer science, including, as you've seen, in Programming Languages.

The free textbook is at
  https://ocw.mit.edu/courses/6-042j-mathematics-for-computer-science-spring-2015/mit6_042js15_textbook.pdf

There are also videos and other materials at 
  https://ocw.mit.edu/courses/6-042j-mathematics-for-computer-science-fall-2010/download/

Some highlights:

1. Immediately relevant to Rocq types and Propositions as Types: Sec 1.4.1, then Chapter 3 until 3.5

2. Logical deductions (Sec 1.4.1) and various kinds of proofs: Sec 1.5--1.9

3. Predicates with quantifiers: 3.6--end of Chapter 3.

4. Induction proofs: Chapter 5. Classic example of an inductive proof "for all natural numbers", Theorem 5.1.2.