

Ask HN - Why 3SAT? - bartonfink

Hey, everyone -<p>The recent buzz over the 3SAT paper has brought an unanswered ? from college back to the front of my mind, and I was hoping someone else could help me out.<p>I understand SAT as a problem and its implications for P/NP. What I'm not clear on, and which my computational complexity professor couldn't/wouldn't elaborate on, is why 3SAT is the "interesting" form of this problem to use?<p>Conceptually, using clauses makes sense because it allows us to express the logical relationship between literals, but why is it useful to restrict clauses to 3 booleans? Why not 2? Why not 5? What's magic about 3?
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RiderOfGiraffes
Because 2-SAT is polynomial. 3-SAT is the smallest "interesting" flavor of the
SAT family. Limiting the forms makes some sorts of reasoning easier, but 3-SAT
and k-SAT are effectively the same. There are simple ways of inter-converting.

ADDED IN EDIT: <http://en.wikipedia.org/wiki/2-satisfiability>

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bartonfink
Okay - that 2-SAT fact makes sense. Thanks!

