--- /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_lt_minus.ma".
+include "ground/arith/ynat_lminus.ma".
+include "ground/arith/ynat_le.ma".
+include "ground/arith/ynat_lt.ma".
+
+(* STRICT ORDER FOR NON-NEGATIVE INTEGERS WITH INFINITY *********************)
+
+(* Cobstructions with yle and ylminus **************************************)
+
+(*** monotonic_ylt_minus_dx *)
+lemma ylt_lminus_bi_dx (o) (x) (y):
+ x < y → yinj_nat o ≤ x → x - o < y - o.
+#o #x #y * -x -y
+/4 width=1 by ylt_inj, yle_inv_inj_bi, nlt_minus_bi_dx/
+qed.