proposition: Lemma remove_dup : forall T eq, forall l1 l2 : list T, forall x, LIn x l1 -> diff eq l1 l2 = remove eq x (diff eq l1 l2).
proof: Proof. induction l1; simpl; sp; subst. rewrite diff_remove. rewrite <- remove_repeat; auto. Qed.
imports: UsefulTypes bin_rels Omega