Problem:
 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)

Proof:
 Containment Processor: loop length: 1
                        terms:
                         from(X)
                        context: cons(X,[])
                        substitution:
                         X -> s(X)
  Qed