(* This file is copied from RamifyCoq project. *)
Require Coq.Setoids.Setoid.
Require Export Coq.Classes.Equivalence.
Require Export Coq.Sets.Ensembles.
intros.
split; intros [].
Qed.

Lemma Empty_set_iff: forall U x, Ensembles.In U (Empty_set U) x <-> False.