--- /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_rplus_succ.ma".
+include "ground/arith/nat_plus.ma".
+
+(* ADDITION FOR NON-NEGATIVE INTEGERS ***************************************)
+
+(* Constructions with rplus *************************************************)
+
+lemma nrplus_inj_sn (p) (n):
+ ninj (p + n) = ninj p + n.
+#p #n @(nat_ind_succ … n) -n //
+#n #IH <nplus_succ_dx <IH //
+qed.
+
+(* Constructions with rplus and npsucc **************************************)
+
+lemma nrplus_npsucc_sn (m) (n):
+ npsucc (m + n) = npsucc m + n.
+#m @(nat_ind_succ … m) -m //
+#m #IH #n <npsucc_succ <nrplus_succ_sn //
+qed.