Properties NP is closed under union, intersection, concatenation, Kleene star and reversal. It is not known whether NP is closed under complement (this question is the so-called "NP versus co-NP" question).
Properties NP i,s closed under union intersection, concatenation Kleene star and reversal. It is not known whether NP is closed under ,complement (this question is the. so-called "NP versus co-NP" question)