LIPIcs.SAT.2024.20.pdf
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It has become standard that, when a SAT solver decides that a CNF Γ is unsatisfiable, it produces a certificate of unsatisfiability in the form of a refutation of Γ in some proof system. The system typically used is DRAT, which is equivalent to extended resolution (ER) - for example, until this year DRAT refutations were required in the annual SAT competition. Recently [Bogaerts et al. 2023] introduced a new proof system, associated with the tool VeriPB, which is at least as strong as DRAT and is further able to handle certain symmetry-breaking techniques. We show that this system simulates the proof system G₁, which allows limited reasoning with QBFs and forms the first level above ER in a natural hierarchy of proof systems. This hierarchy is not known to be strict, but nevertheless this is evidence that the system of [Bogaerts et al. 2023] is plausibly strictly stronger than ER and DRAT. In the other direction, we show that symmetry-breaking for a single symmetry can be handled inside ER.
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