Is the class NP closed under complement?

Problem Detail: 

Is the class $\sf NP$ closed under complement or is it unknown? I have looked online, but I couldn't find anything.

Asked By : user16742

Answered By : joebloggs

The answer is "not known to science". It is known that P is closed under complement. So if P = NP then NP is closed under complement as well. Also, if NP is not closed under complement, then P != NP.

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Question Source : http://cs.stackexchange.com/questions/24261