Many problems in CS can be reduced to checking satisfiability of a propositional calculus formula.

Two efficient algorithms for satisfiability checking (SAT):

• The Davis-Putnam or DPLL algorithm uses heuristics for early termination (determining the value from a partially specified model), pure symbols (those that have the same sign in all clauses) and unit clauses (those with a single literal).

  The CHAFF inplementation of DPLL solves hardware verification problems with a million variables.

• The WalkSAT algorithm uses a combination of hill climbing (selecting a literal assignment that makes the most clauses true) and random steps.

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