--- /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/notation/functions/element_i_0.ma".
+include "ground/relocation/gr_map.ma".
+
+(* IDENTITY ELEMENT FOR GENERIC RELOCATION MAPS ******************************************************)
+
+(*** id *)
+corec definition gr_id: gr_map ≝ ⫯gr_id.
+
+interpretation
+ "identity element (generic relocation streams)"
+ 'ElementI = (gr_id).
+
+(* Basic properties (specific) *********************************************************)
+
+(*** id_rew *)
+lemma gr_id_unfold: ⫯𝐢 = 𝐢.
+<(stream_unfold … (𝐢)) in ⊢ (???%); //
+qed.