Strong Conflict Analysis for Propositional Satisfiability

We present a new approach to conflict analysis for propositional satisfiability solvers based on the DPLL procedure and clause recording. When conditions warrant it, we generate a supplemental clause from a conflict. This clause does not contain a unique implication point, and therefore cannot replace the standard conflict clause. However, it is very effective at reducing excessive depth in the implication graphs and at preventing repeated conflicts on the same clause. Experimental results show consistent improvements over state-of-the-art solvers and confirm our analysis of why the new technique works.