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Unformatted text preview: variables that satisfy all the clauses)? If so, give a satisfying assignment. b. Is this formula satisfiable? A => b C and d => a => A C => d Satisfiable: A true B true C false D false But adding the single clause a => c makes he formula unsatisfiable. c. Greedy strategy Start with all variables false Make a variable true only if forced to by some implication If all negative clasues are satisfied output assignment Else output not satifiable A => b C and d => a => a C => d A b c d False false false false True “ “ “ “ true “ “ d. Why is this correct? At the end of phase 1, if a variable is set to true, then it must be true in any satisfying assignment. Minimal # of true variables If phase 2 fails, it is because a negative clause wants us to make some variable false. But this is not possible. e....
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- Spring '08
- Algorithms, Conjunctive normal form, Boolean satisfiability problem, Horn clause, negative clause, Horn Satisfiability, Horn-satisfiability