They are the ones with the property found by Cook, Karp and Levin: If an efficient algorithm for any one of them were found, it could be adapted to solve all the other NP problems as well.

• 这类问题具有库克、卡普与李文所发现的性质：如果可以找到其中一个问题的有效演算法，就能修改这个演算法，解决所有其他的NP问题。