Problem:
 incr(nil()) -> nil()
 incr(cons(X,L)) -> cons(s(X),incr(L))
 adx(nil()) -> nil()
 adx(cons(X,L)) -> incr(cons(X,adx(L)))
 nats() -> adx(zeros())
 zeros() -> cons(0(),zeros())
 head(cons(X,L)) -> X
 tail(cons(X,L)) -> L

Proof:
 Containment Processor: loop length: 1
                        terms:
                         zeros()
                        context: cons(0(),[])
                        substitution:
                         
  Qed