update in ground

[helm.git] / matita / matita / contribs / lambdadelta / ground / arith / nat_pred_succ.ma

diff --git a/matita/matita/contribs/lambdadelta/ground/arith/nat_pred_succ.ma b/matita/matita/contribs/lambdadelta/ground/arith/nat_pred_succ.ma
index 4a6e23b01846b0fd7b807b095b87add5b44d060f..5472d7c1bee0a348a9233f491f820c9c7bd37030 100644 (file)
--- a/matita/matita/contribs/lambdadelta/ground/arith/nat_pred_succ.ma
+++ b/matita/matita/contribs/lambdadelta/ground/arith/nat_pred_succ.ma
@@ -43,6 +43,15 @@ lemma npred_succ (n): n = ↓↑n.
 * //
 qed.
 
+(* Basic inversions *********************************************************)
+
+lemma eq_inv_pnpred_bi:
+      injective … pnpred.
+#p1 #p2 #Hp
+>(npsucc_pred p1) >(npsucc_pred p2)
+<Hp -Hp @refl
+qed-.
+
 (* Inversions with nsucc ****************************************************)
 
 (*** nat_split *)