TRS:
 {                from(X) -> cons(X, from(s(X))),
            first(0(), Z) -> nil(),
  first(s(X), cons(Y, Z)) -> cons(Y, first(X, Z)),
     sel(0(), cons(X, Z)) -> X,
    sel(s(X), cons(Y, Z)) -> sel(X, Z)}
 Fail