intros; clear.
unfold eval_cnf in *.
rewrite make_conj_cons ; eauto.
unfold eval_clause.
tauto.
Qed.

Lemma or_cnf_opt_correct : forall env f f', eval_cnf env (or_cnf_opt f f') <-> eval_cnf env (or_cnf f f').
Variable eval  : Env -> forall (k: kind), Term -> rtyp k.