proposition: Lemma lang_equiv: forall L1 L2, Equiv L1 L2 -> forall m, Recognizes m L1 <-> Recognizes m L2.
proof: Proof. split; unfold Recognizes; intros. - rewrite H0. auto. - rewrite H0. symmetry. auto. Qed.
imports: Coq.Setoids.Setoid Coq.Bool.Bool Coq.Logic.Classical_Prop