(* SUCCESSOR FOR NON-NEGATIVE INTEGERS **************************************)
-(* Rewrites with ntri *******************************************************)
+(* Constructions with ntri **************************************************)
+
+lemma ntri_zero_succ (A) (a1) (a2) (a3) (n):
+ a1 = ntri A (𝟎) (↑n) a1 a2 a3.
+#A #a1 #a2 #a3 * //
+qed.
+
+lemma ntri_succ_zero (A) (a1) (a2) (a3) (n):
+ a3 = ntri A (↑n) (𝟎) a1 a2 a3.
+#A #a1 #a2 #a3 * //
+qed.
lemma ntri_succ_bi (A) (a1) (a2) (a3) (n1) (n2):
ntri A (n1) (n2) a1 a2 a3 = ntri A (↑n1) (↑n2) a1 a2 a3.