Counterexample-Guided Model Synthesis

In this paper we present a new approach for solving quantified formulas in Satisfiability Modulo Theories (SMT), with a particular focus on the theory of fixed-size bit-vectors. We combine counterexample-guided quantifier instantiation with a syntax-guided synthesis approach, which allows us to synthesize both Skolem functions and terms for quantifier instantiations. Our approach employs two ground theory solvers to reason about quantified formulas. It neither relies on quantifier specific simplifications nor heuristic quantifier instantiation techniques, which makes it a simple yet effective approach for solving quantified formulas. We implemented our approach in our SMT solver Boolector and show in our experiments that our techniques are competitive compared to the state-of-the-art in solving quantified bit-vectors.