--- /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 *)
+(* *)
+(**************************************************************************)
+
+include "ground/lib/subset.ma".
+include "ground/notation/relations/between_3.ma".
+include "ground/notation/relations/not_between_3.ma".
+
+(* OVERLAP FOR SUBSETS ******************************************************)
+
+definition subset_ol (A): relation2 (𝒫❨A❩) (𝒫❨A❩) ≝
+ λu1,u2. ∃∃p. p ϵ u1 & p ϵ u2.
+
+interpretation
+ "overlap (subset)"
+ 'Between A u1 u2 = (subset_ol A u1 u2).
+
+interpretation
+ "negated overlap (subset)"
+ 'NotBetween A u1 u2 = (negation (subset_ol A u1 u2)).
+
+(* Basic constructions ******************************************************)
+
+lemma subset_ol_i (A) (u1) (u2) (a):
+ a ϵ u1 → a ϵ u2 → u1 ≬{A} u2.
+/2 width=3 by ex2_intro/ qed.
--- /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 *)
+(* *)
+(**************************************************************************)
+
+(* GROUND NOTATION **********************************************************)
+
+notation < "hvbox( a ≬ break term 46 u )"
+ non associative with precedence 45
+ for @{ 'Between $S $a $u }.
+
+notation > "hvbox( a ≬ break term 46 u )"
+ non associative with precedence 45
+ for @{ 'Between ? $a $u }.
+
+notation > "hvbox( a ≬{ break term 46 S } break term 46 u )"
+ non associative with precedence 45
+ for @{ 'Between $S $a $u }.
--- /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 *)
+(* *)
+(**************************************************************************)
+
+(* GROUND NOTATION **********************************************************)
+
+notation < "hvbox( a ⧸≬ break term 46 u )"
+ non associative with precedence 45
+ for @{ 'NotBetween $S $a $u }.
+
+notation > "hvbox( a ⧸≬ break term 46 u )"
+ non associative with precedence 45
+ for @{ 'NotBetween ? $a $u }.
+
+notation > "hvbox( a ⧸≬{ break term 46 S } break term 46 u )"
+ non associative with precedence 45
+ for @{ 'NotBetween $S $a $u }.