On Deciding Satisfiability by Theorem Proving with Speculative Inferences

Applications in software verification often require determining the satisfiability of first-order formulae with respect to background theories. During development, conjectures are usually false. Therefore, it is desirable to have a theorem prover that terminates on satisfiable instances. Satisfiability Modulo Theories (SMT) solvers have proven to be highly scalable, efficient and suitable for integrated theory reasoning. Inference systems with resolution and superposition are strong at reasoning with equalities, universally quantified variables, and Horn clauses. We describe a theorem-proving method that tightly integrates superposition-based inference system and SMT solver. The combination is refutationally complete if background theory symbols only occur in ground formulae, and non-ground clauses are variable-inactive. Termination is enforced by introducing additional axioms as hypotheses. The system detects any unsoundness introduced by these speculative inferences and recovers from it.