Problem:
 f(X) -> cons(X,f(g(X)))
 g(0()) -> s(0())
 g(s(X)) -> s(s(g(X)))
 sel(0(),cons(X,Y)) -> X
 sel(s(X),cons(Y,Z)) -> sel(X,Z)

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