versat: A verified modern SAT solver. This paper presents versat, a formally verified SAT solver incorporating the essential features of modern SAT solvers, including clause learning, watched literals, optimized conflict analysis, non-chronological backtracking, and decision heuristics. Unlike previous related work on SAT-solver verification, our implementation uses efficient low-level data structures like mutable C arrays for clauses and other solver state, and machine integers for literals. The implementation and proofs are written in Guru, a verified-programming language. We compare versat to a state-of-the-art SAT solver that produces certified “unsat” answers. We also show through an empirical evaluation that versat can solve SAT problems on the modern scale.