MAYBE MAYBE TRS: { from(X) -> cons(X, n__from(n__s(X))), from(X) -> n__from(X), sel(0(), cons(X, Y)) -> X, sel(s(X), cons(Y, Z)) -> sel(X, activate(Z)), activate(X) -> X, activate(n__from(X)) -> from(activate(X)), activate(n__s(X)) -> s(activate(X)), s(X) -> n__s(X) } DUP: We consider a duplicating system. Trs: { from(X) -> cons(X, n__from(n__s(X))), from(X) -> n__from(X), sel(0(), cons(X, Y)) -> X, sel(s(X), cons(Y, Z)) -> sel(X, activate(Z)), activate(X) -> X, activate(n__from(X)) -> from(activate(X)), activate(n__s(X)) -> s(activate(X)), s(X) -> n__s(X) } Fail