Complete and Efficient DRAT Proof Checking

DRAT proofs have become the standard for verifying unsatisfiability proofs emitted by modern SAT solvers. However, recent work showed that the specification of the format differs from its implementation in existing tools due to optimizations necessary for efficiency. Although such differences do not compromise soundness of DRAT checkers, the sets of correct proofs according to the specification and to the implementation are incomparable. We discuss how it is possible to design DRAT checkers faithful to the specification by carefully modifying the standard optimization techniques. We implemented such modifications in a configurable DRAT checker. Our experimental results show negligible overhead due to these modifications, suggesting that efficient verification of the DRAT specification is possible. Furthermore, we show that the differences between specification and implementation of DRAT often arise in practice.