What are the problems that are in co-NP but not in NP?i.e, those problems where incorrect strings can be deterministically verified in polynomial time but the correct strings can't be.
co-NP but not NP problems
p vs np;co np
co-NP is the set of complements of problems that are in NP. So co-NP contains problems such as non-3-colourability, Boolean unsatisfiability and so on.Most complexity theorists believe that NP$\,\neq\,$co-NP and one consequence of this is that the complement of any NP-complete problem would be in co-NP but not in NP.Wikipedia has more information on co-NP.