(* STRICT ORDER FOR NON-NEGATIVE INTEGERS ***********************************)
-(* Rewrites with nminus *****************************************************)
+(* Constructions with nminus ************************************************)
+
+(*** monotonic_lt_minus_l *)
+lemma nlt_minus_sn_bi (o) (m) (n): o ≤ m → m < n → m - o < n - o.
+#o #m #n #Hom #Hmn
+lapply (nle_minus_sn_bi … o Hmn) -Hmn
+<(nminus_succ_sn … Hom) //
+qed.
+
+(* Destructions with nminus *************************************************)
(*** minus_pred_pred *)
lemma nminus_pred_bi (m) (n): 𝟎 < m → 𝟎 < n → n - m = ↓n - ↓m.
//
qed-.
-(* Constructions with nminus ************************************************)
-
-(*** monotonic_lt_minus_l *)
-lemma nlt_minus_sn_bi (o) (m) (n): o ≤ m → m < n → m - o < n - o.
-#o #m #n #Hom #Hmn
-lapply (nle_minus_sn_bi … o Hmn) -Hmn
-<(nminus_succ_sn … Hom) //
-qed.
+lemma nlt_des_minus_dx (o) (m) (n): m < n - o → o < n.
+#o @(nat_ind_succ … o) -o
+[ #m #n <nminus_zero_dx
+ /2 width=3 by le_nlt_trans/
+| #o #IH #m #n <nminus_succ_dx_pred_sn #H
+ /3 width=2 by nlt_inv_pred_dx/
+]
+qed-.