Proofs and proof checking is also big in SAT solving (think: MiniSat) and SMT (think: z3, cvc5). It's also coming to model counting (counting the number of solutions). In fact, we did one in Isabelle for an approximate model counter [1], that provides probabilistically approximate count (a so-called PAC guarantee), which is a lot harder to do, due to the probabilistic nature.
[1] https://github.com/meelgroup/approxmc