permutation_rec1([X|Y],Z) :-
  permutation_rec1(Y,W),
  select(X,Z,W).
permutation_rec1([],[]).

permutation_rec2([], []).
permutation_rec2([X], [X]) :-!.
permutation_rec2([T|H], X) :-
  permutation_rec2(H, H1),
  append(L1, L2, H1),
  append(L1, [T], X1),
  append(X1, L2, X).