update in delayed_updating

[helm.git] / matita / matita / contribs / lambdadelta / ground / lib / list_append.ma

diff --git a/matita/matita/contribs/lambdadelta/ground/lib/list_append.ma b/matita/matita/contribs/lambdadelta/ground/lib/list_append.ma
index 13c68a33cb38843ec0f184012af2d3a4a803eac8..05fefceb30a13e1f9fcbd5727f728b7ce11ec1b9 100644 (file)
--- a/matita/matita/contribs/lambdadelta/ground/lib/list_append.ma
+++ b/matita/matita/contribs/lambdadelta/ground/lib/list_append.ma
@@ -56,3 +56,14 @@ lemma list_append_assoc (A):
   ]
 ]
 qed.
+
+(* Basic inversions *********************************************************)
+
+lemma eq_inv_list_empty_append (A):
+      ∀l1,l2. ⓔ = l1⨁{A}l2 →
+      ∧∧ ⓔ = l1 & ⓔ = l2.
+#A *
+[ #l2 /2 width=1 by conj/
+| #a1 #l1 #l2 <list_append_lcons_sn #H destruct
+]
+qed-.