X-Git-Url: http://matita.cs.unibo.it/gitweb/?a=blobdiff_plain;f=matita%2Fmatita%2Fcontribs%2Flambdadelta%2Fground_2%2Fynat%2Fynat_lt.ma;h=26135550e71f510781a6a03f19a09206b996503d;hb=5d669f492522b055f76c627eb89da97d0be05c2a;hp=a306b57562a05fb302bbebad255f28ce61465a55;hpb=d95bd78c09617ad212fa9e96837a15fc907dcfca;p=helm.git

diff --git a/matita/matita/contribs/lambdadelta/ground_2/ynat/ynat_lt.ma b/matita/matita/contribs/lambdadelta/ground_2/ynat/ynat_lt.ma
index a306b5756..26135550e 100644
--- a/matita/matita/contribs/lambdadelta/ground_2/ynat/ynat_lt.ma
+++ b/matita/matita/contribs/lambdadelta/ground_2/ynat/ynat_lt.ma
@@ -122,6 +122,13 @@ lemma ylt_O: ∀x. ⫯⫰(yinj x) = yinj x → 0 < x.
 #H destruct
 qed.
 
+(* Properties on predecessor ************************************************)
+
+lemma ylt_pred: ∀m,n. m < n → 0 < m → ⫰m < ⫰n.
+#m #n * -m -n
+/4 width=1 by ylt_inv_inj, ylt_inj, monotonic_lt_pred/
+qed.
+
 (* Properties on successor **************************************************)
 
 lemma ylt_O_succ: ∀n. 0 < ⫯n.