--- /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/relocation/gr_tls.ma".
+include "ground/relocation/gr_sor.ma".
+
+(* RELATIONAL UNION FOR GENERIC RELOCATION MAPS ***********************************************************)
+
+(* Properties with iterated tail ********************************************)
+
+(*** sor_tls *)
+lemma gr_sor_tls:
+ ∀f1,f2,f. f1 ⋓ f2 ≘ f →
+ ∀n. ⫱*[n]f1 ⋓ ⫱*[n]f2 ≘ ⫱*[n]f.
+#f1 #f2 #f #Hf #n @(nat_ind_succ … n) -n
+/2 width=1 by gr_sor_tl/
+qed.