title: How is 2-CNF SAT is in P, while 3-CNF SAT is in NPC?
body: <p>I am really confused why 2-CNF SAT is in P, while 3-CNF SAT is in NPC. I Read CLRS, and I understand how they prove 3-CNF SAT is in NPC. Can't I use the same reducibility from SAT to 2-CNF-SAT to prove 2-CNF-SAT is in NPC. I don't understand why 2-CNF SAT is in P.</p>