proposition: Lemma cnf_plus : forall ol alpha, is_cnf_of alpha ol -> forall ol' beta, is_cnf_of beta ol' -> exists ol'', is_cnf_of (alpha + beta) ol''.
proof: Proof. destruct 1 as [H H0]. destruct 1 as [H1 H2]. rewrite H0;rewrite H2; apply cnf_plus2;auto. Qed.
imports: Coq(Arith List Sorting.Sorted Logic.Epsilon Ensembles)