--- /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 *)
+(* *)
+(**************************************************************************)
+
+set "baseuri" "cic:/matita/RELATIONAL/NLE/inv".
+
+include "NPlus/inv.ma".
+include "NLE/defs.ma".
+
+theorem nle_inv_succ_1: \forall x,y. x < y \to
+ \exists z. y = succ z \land x <= z.
+ intros. elim H.
+ lapply linear nplus_gen_succ_2 to H1.
+ decompose. subst. auto depth = 4.
+qed.
+
+theorem nle_inv_succ_succ: \forall x,y. x < succ y \to x <= y.
+ intros.
+ lapply linear nle_inv_succ_1 to H. decompose.
+ destruct H1. clear H1. subst.
+ auto.
+qed.
+
+theorem nle_inv_succ_zero: \forall x. x < zero \to False.
+ intros.
+ lapply linear nle_inv_succ_1 to H. decompose.
+ destruct H1.
+qed.
+
+theorem nle_inv_zero_2: \forall x. x <= zero \to x = zero.
+ intros 1. elim x; clear x; intros;
+ [ auto
+ | lapply linear nle_inv_succ_zero to H1. decompose.
+ ].
+qed.
+
+theorem nle_inv_succ_2: \forall y,x. x <= succ y \to
+ x = zero \lor \exists z. x = succ z \land z <= y.
+ intros 2; elim x; clear x; intros;
+ [ auto
+ | lapply linear nle_inv_succ_succ to H1.
+ auto depth = 4.
+ ].
+qed.