PERMUTATION IN PROLOG

delete(X,[X|Tail],Tail).

delete(X,[Y|Tail],[Y|Tail1]):-delete(X,Tail,Tail1).

insert(X,List,B):-delete(X,B,List).

per([],[]).

per([X|L],P):-per(L,L1),insert(X,L1,P).

 Output

 per([a,b,c],P).

 P=["a","b","c"]

 P=["b","a","c"]

 P=["b","c","a"]

 P=["a","c","b"]

 P=["c","a","b"]

 P=["c","b","a"]