--- /dev/null
+(**************************************************************************)
+(* ___ *)
+(* ||M|| *)
+(* ||A|| A project by Andrea Asperti *)
+(* ||T|| *)
+(* ||I|| Developers: *)
+(* ||T|| A.Asperti, C.Sacerdoti Coen, *)
+(* ||A|| E.Tassi, S.Zacchiroli *)
+(* \ / *)
+(* \ / This file is distributed under the terms of the *)
+(* v GNU Lesser General Public License Version 2.1 *)
+(* *)
+(**************************************************************************)
+
+set "baseuri" "cic:/matita/higher_order_defs/relations/".
+
+include "logic/connectives.ma".
+
+definition relation : Type \to Type
+\def \lambda A:Type.A \to A \to Prop.
+
+definition reflexive: \forall A:Type.\forall R :relation A.Prop
+\def
+\lambda A.\lambda R.\forall x:A.R x x.
+
+definition symmetric: \forall A:Type.\forall R: relation A.Prop
+\def
+\lambda A.\lambda R.\forall x,y:A.R x y \to R y x.
+
+definition transitive: \forall A:Type.\forall R:relation A.Prop
+\def
+\lambda A.\lambda R.\forall x,y,z:A.R x y \to R y z \to R x z.
+
+definition irreflexive: \forall A:Type.\forall R:relation A.Prop
+\def
+\lambda A.\lambda R.\forall x:A.\lnot (R x x).
+
+definition cotransitive: \forall A:Type.\forall R:relation A.Prop
+\def
+\lambda A.\lambda R.\forall x,y:A.R x y \to \forall z:A. R x z \lor R z y.
+
+definition tight_apart: \forall A:Type.\forall eq,ap:relation A.Prop
+\def
+\lambda A.\lambda eq,ap.\forall x,y:A. (\not (ap x y) \to eq x y) \land
+(eq x y \to \not (ap x y)).
+
+definition antisymmetric: \forall A:Type.\forall R:relation A.Prop
+\def
+\lambda A.\lambda R.\forall x,y:A. R x y \to \not (R y x).
+
+