Along the same lines, co-NP is the class containing the complement problems (i.e. problems with the yes/no answers reversed) of NP problems. Source: Internet
From this it follows that the set of complements of the problems in NP is a subset of the set of complements of the problems in co-NP, i.e., co-NP NP. Source: Internet
In fact, it is an open question whether all problems in NP also have certificates for the "no"-answers and thus are in co-NP. Source: Internet
Note that the tautology problem for positive Boolean formulae remains co-NP complete, even though the satisfiability problem is trivial, as every positive Boolean formula is satisfiable. Source: Internet
If is different from co-NP, then all of the co-NP complete problems are not solvable in polynomial time. Source: Internet
See co-NP and NP-complete for more details. Source: Internet