Fahiem Bacchus, University of Toronto
The backtracking based Davis Putnam (DPLL) procedure remains the dominant method for deciding the satisfiability of a CNF formula. In recent years there has been much work on improving the basic procedure by adding features like improved heuristics and data structures, intelligent backtracking, clause learning, etc. Reasoning with binary clauses in DPLL has been a much discussed possibility for achieving improved performance, but to date solvers based on this idea have not been competitive with the best unit propagation based DPLL solvers. In this paper we experiment with a DPLL solver called 2cls+eq that makes more extensive use of binary clause reasoning than has been tried before. The results are very encouraging---2cls+eq is competitive with the very best DPLL solvers. The techniques it uses also open up a number of other possibilities for increasing our ability to solve SAT problems.