proposition: Lemma set_remove_one_add_same : forall E x, x \notin E -> E = (E \u \{x}) \-- x.
proof: Proof. Proof using. introv Hx. set_unf. extens. iff. { split. eauto. intro. subst*. } { tauto. } Qed.
imports: Coq.Classes.Morphisms TLC(LibTactics LibLogic LibReflect LibList LibOperation LibMonoid LibInt LibNat LibEpsilon LibRelation LibMin)