Problem:
 tail(cons(X)) -> XS
 nats() -> cons(0())
 pairs() -> cons(0())
 odds() -> incr(pairs())
 incr(cons(X)) -> cons(s(X))
 head(cons(X)) -> X

Proof:
 Fresh Variable Processor:
  loop length: 1
  terms:
   tail(cons(X))
  context: []
  substitution:
   XS -> tail(cons(X))
  Qed