CNF vs Horn Satisfiability

Question

I know that it's easier to prove if a horn-formula is satisfiable. My Question is: Why is it easier with a horn formula rather than a normal CNF?

score 1 · Accepted Answer · edited Dec 09 '18 at 05:34

1

Presence or absence of Horn satisfiability can be shown in linear time. Here is a good introduction with some examples. The solution can be found by unit propagation without backtracking.

Pseudocode from a UC Berkeley lecture note:

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Satisfiability for general CNF expressions is a classic NP-complete problem. No polynomial time algorithms are known for CNF satisfiability (except if P=NP).

edited Dec 09 '18 at 05:34

Emerson Hsieh

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answered Mar 18 '15 at 17:41

Axel Kemper

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CNF vs Horn Satisfiability

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