Some notation and additional lemmata.

[helm.git] / helm / software / matita / library / list / list.ma

diff --git a/helm/software/matita/library/list/list.ma b/helm/software/matita/library/list/list.ma
index 19866cc2992499df10a53a9c0fba8766458c601f..077e1af6c443682939461692d20bdfc20f60be22 100644 (file)
--- a/helm/software/matita/library/list/list.ma
+++ b/helm/software/matita/library/list/list.ma
@@ -195,3 +195,9 @@ intros;elim l
      [simplify;apply le_S_S;assumption
      |simplify;apply le_S;assumption]]
 qed.
+
+lemma length_append : ∀A,l,m.length A (l@m) = length A l + length A m.
+intros;elim l
+[reflexivity
+|simplify;rewrite < H;reflexivity]
+qed.