Verified and Optimized Implementation of Orthologic Proof Search

Abstract

Abstract We report on the development of an optimized and verified decision procedure for orthologic equalities and inequalities. This decision procedure is quadratic-time and is used as a sound, efficient and predictable approximation to classical propositional logic in automated reasoning tools. We formalize, in the Coq proof assistant, a proof system in sequent-calculus style for orthologic. We then prove its soundness and completeness with respect to the algebraic variety of ortholattices, and we formalize a cut-elimination theorem. In doing so, we discover and fix a missing case in a previously published proof. We then implement and verify a complete proof search procedure for orthologic. A naive implementation is exponential; to obtain an optimal quadratic run time, we optimize the implementation by memoizing its results and simulating reference equality testing. We leverage the resulting correctness theorem to implement a reflective Coq tactic. We present benchmarks showing that the procedure, under various optimizations, matches its theoretical complexity. Finally, we develop a collection of tactics, including normalization with respect to orthologic and a boolean solver, which we also benchmark. We make tactics available as a standalone Coq plugin.