This in the definition of NPC. What you have to prove is that a language is in NPC. This was proved for SAT first: http://en.wikipedia.org/wiki/Cook%E2%80%93Le

This in the definition of NPC. What you have to prove is that a language is in NPC. This was proved for SAT first: http://en.wikipedia.org/wiki/Cook%E2%80%93Levin_theorem http://en.wikipedia.org/wiki/Cook%E2%80%93Levin_theorem http://en.wikipedia.org/wiki/NP_complete http://en.wikipedia.org/wiki/NP_complete