Classical STRIPS-style planning problems are formulated as theorems to be proven from a new point of view. The result for a refutation-based theorem prover may be a propositional formula that is to be proven unsatisfiable. This formula is identical to the formula that may be derived directly by various "sat compilers", but the theorem-proving view provides valuable additional information not in the formula: namely, the theorem to be proven. Traditional satisfiability methods, most of which are based on model search, are unable to exploit this additional information. However, a new algorithm, called "Modoc", is able to exploit this information and has achieved performance comparable or superior to the fastest known satisfiability methods, including stochastic search methods, on planning problems that have been reported by other researchers, as well as formulas derived from other applications. Unlike most theorem provers, Modoc performs well on both satisfiable and unsatisfiable formulas...

Model elimination is a back-chaining strategy to search for and construct resolution refutations. Many formulas can be refuted more succinctly by recording certain derived clauses, called lemmas, then using them where a clause of the original formula would normally be required. However, recording too many lemmas overwhelms the proof search.