MAYBE
Trs:
 {             first(0(), X) -> nil(),
     first(s(X), cons(Y, Z)) -> cons(Y, n__first(X, activate(Z))),
               first(X1, X2) -> n__first(X1, X2),
                     from(X) -> cons(X, n__from(n__s(X))),
                     from(X) -> n__from(X),
                        s(X) -> n__s(X),
  activate(n__first(X1, X2)) -> first(activate(X1), activate(X2)),
        activate(n__from(X)) -> from(activate(X)),
           activate(n__s(X)) -> s(activate(X)),
                 activate(X) -> X}
 Comment:
  We consider a duplicating trs.
  FAIL:
   Open