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