proposition: Theorem NoDup_gen_eq : forall (A : Type)(ls : list A), NoDup ls <-> NoDup_gen eq ls.
proof: Proof. induction ls; intuition; simpl in *. econstructor. econstructor. inversion H1; clear H1; subst. econstructor. intuition. eapply H4. eapply In_gen_eq. trivial. intuition. inversion H1; clear H1; subst. econstructor. intuition. eapply H4. eapply In_gen_eq. trivial. intuition. Qed.
imports: List FCF.Fold