Squolem

Validating QBF invalidity in HOL4. The Quantified Boolean Formulae (QBF) solver Squolem can generate certificates of invalidity, based on Q-resolution. We present independent checking of these certificates in the HOL4 theorem prover. This enables HOL4 users to benefit from Squolem’s automation for QBF problems, and provides high correctness assurances for Squolem’s results. Detailed performance data shows that LCF-style certificate checking is feasible even for large QBF instances. Our work prompted improvements to HOL4’s inference kernel.