proposition: Lemma Sort_In_eq : forall xs ys, Sort xs -> Sort ys -> (forall a, In a xs <-> In a ys) -> xs = ys.
proof: Proof. Proof with auto using In_InA, InA_In. intros ? ? ? ? H. apply Sort_InA_eq... intros a; specialize (H a). split; intros; apply In_InA; intuition... Qed.
imports: Coq.Lists.List Coq.Lists.SetoidList Metalib.CoqUniquenessTac