complementary nondeterministic polynomial definition complexity
(Co-NP) The set (or property) of problems with a yes/no answer where the complementary no/yes problem takes nondeterministic polynomial time
For example, "Is n prime" is Co-NP and "Is n not prime" is NP, since it is only necessary to find one factor
to prove that n is not prime
whereas to prove that it is prime all possible factors must be eliminated.