--- /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/arith/nat_minus_plus.ma".
+include "ground/relocation/fr2_map.ma".
+
+(* ADDITION FOR FINITE RELOCATION MAPS WITH PAIRS ******************************)
+
+(* Note: this is pushs *)
+(*** pluss *)
+rec definition fr2_plus (f:fr2_map) (n:nat) on f ≝ match f with
+[ fr2_nil ⇒ ◊
+| fr2_cons d h f ⇒ ❨d+n,h❩;fr2_plus f n
+].
+
+interpretation
+ "plus (finite relocation maps with pairs)"
+ 'plus f n = (fr2_plus f n).
+
+(* Basic properties *********************************************************)
+
+(*** pluss_SO2 *)
+lemma fr2_plus_cons_unit (d) (h) (f):
+ ((❨d,h❩;f)+𝟏) = ❨↑d,h❩;f+𝟏.
+normalize // qed.
+
+(* Basic inversion lemmas ***************************************************)
+
+(*** pluss_inv_nil2 *)
+lemma fr2_plus_inv_nil_dx (n) (f):
+ f+n = ◊ → f = ◊.
+#n * // normalize
+#d #h #f #H destruct
+qed.
+
+(*** pluss_inv_cons2 *)
+lemma fr2_plus_inv_cons_dx (n) (d) (h) (f2) (f):
+ f + n = ❨d,h❩;f2 →
+ ∃∃f1. f1+n = f2 & f = ❨d-n,h❩;f1.
+#n #d #h #f2 *
+[ normalize #H destruct
+| #d1 #h1 #f1 whd in ⊢ (??%?→?); #H destruct
+ <nminus_plus_sn_refl_sn /2 width=3 by ex2_intro/
+]
+qed-.