Problem:
 filter(cons(X,Y),0(),M) -> cons(0(),filter(Y,M,M))
 filter(cons(X,Y),s(N),M) -> cons(X,filter(Y,N,M))
 sieve(cons(0(),Y)) -> cons(0(),sieve(Y))
 sieve(cons(s(N),Y)) -> cons(s(N),sieve(filter(Y,N,N)))
 nats(N) -> cons(N,nats(s(N)))
 zprimes() -> sieve(nats(s(s(0()))))

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