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when toggle format what by license comment
Mar 27, 2013 at 18:44 comment added frafl You have to show that NP is closed under concatenation too.
Feb 20, 2013 at 20:42 vote accept Mirrana
Feb 15, 2013 at 2:53 history edited Mirrana CC BY-SA 3.0
added 36 characters in body
Feb 15, 2013 at 2:43 history answered Mirrana CC BY-SA 3.0