Efficient modular SAT solving for IC3

We describe an efficient way to compose SAT solvers into chains, while still allowing unit propagation between those solvers. We show how such a “SAT Modulo SAT” solver naturally produces sequence interpolants as a side effect - there is no need to generate a resolution proof and post-process it to extract an interpolant. We have implemented a version of IC3 using this SAT Modulo SAT solver, which solves both more SAT instances and more UNSAT instances than PDR and IC3 on each of the 2008, 2010, and 2012 Hardware Model Checking Competition benchmarks.