Standard Out:

in clause front/oi(tree(X0,L,R),Xs) :-
    front/oo(L,Ls),
    front/oo(R,Rs),
    app/iii(Ls,Rs,Xs).
  variables have no producer: ["X0"]

Standard Err:


real	0m0.446s
user	0m0.264s
sys	0m0.028s