--- /dev/null
+(**************************************************************************)
+(* ___ *)
+(* ||M|| *)
+(* ||A|| A project by Andrea Asperti *)
+(* ||T|| *)
+(* ||I|| Developers: *)
+(* ||T|| The HELM team. *)
+(* ||A|| http://helm.cs.unibo.it *)
+(* \ / *)
+(* \ / This file is distributed under the terms of the *)
+(* v GNU General Public License Version 2 *)
+(* *)
+(**************************************************************************)
+
+set "baseuri" "cic:/matita/PREDICATIVE-TOPOLOGY/class_eq".
+
+include "class_le.ma".
+
+theorem ceq_cl: \forall C,c1,c2. ceq ? c1 c2 \to cin C c1 \land cin C c2.
+intros; elim H; clear H.
+lapply cle_cl to H1 using H; clear H1; decompose H;
+lapply cle_cl to H2 using H; clear H2; decompose H.
+auto.
+qed.
+
+theorem ceq_refl: \forall C,c. cin C c \to ceq ? c c.
+intros; apply ceq_intro; auto.
+qed.
+
+theorem ceq_trans: \forall C,c2,c1,c3.
+ ceq C c2 c3 \to ceq ? c1 c2 \to ceq ? c1 c3.
+intros; elim H; elim H1; clear H; clear H1.
+apply ceq_intro; apply cle_trans; [|auto|auto||auto|auto].
+qed.
+
+theorem ceq_sym: \forall C,c1,c2. ceq C c1 c2 \to ceq C c2 c1.
+intros; elim H; clear H.; auto.
+qed.