- ynat: some additions

[helm.git] / matita / matita / contribs / lambdadelta / ground_2 / ynat / ynat_minus.ma

diff --git a/matita/matita/contribs/lambdadelta/ground_2/ynat/ynat_minus.ma b/matita/matita/contribs/lambdadelta/ground_2/ynat/ynat_minus.ma
index 10a841cbd4f04ba980dc611a0cef4e1b73ced275..596885cf0b55361d538c47008099f3759520aa73 100644 (file)
--- a/matita/matita/contribs/lambdadelta/ground_2/ynat/ynat_minus.ma
+++ b/matita/matita/contribs/lambdadelta/ground_2/ynat/ynat_minus.ma
@@ -38,6 +38,9 @@ qed.
 lemma yminus_O1: ∀x:ynat. 0 - x = 0.
 * // qed.
 
+lemma yminus_refl: ∀x:ynat. x - x = 0.
+* // qed.
+
 lemma yminus_minus_comm: ∀y,z,x. x - y - z = x - z - y.
 * #y [ * #z [ * // ] ] >yminus_O1 //
 qed.