X-Git-Url: http://matita.cs.unibo.it/gitweb/?a=blobdiff_plain;f=matita%2Fmatita%2Fcontribs%2Flambdadelta%2Fdelayed_updating%2Fsyntax%2Fpreterm.ma;h=6406d1dd7e50900f498b1832728315c5701e89e9;hb=41a54a797af98d2867d4bf979d424283fb44a1fc;hp=b7b90a4cf8f40e455866f8dd4c281c4252fbe935;hpb=2cc4eb5d0210be58286e028278852122dcb68052;p=helm.git

diff --git a/matita/matita/contribs/lambdadelta/delayed_updating/syntax/preterm.ma b/matita/matita/contribs/lambdadelta/delayed_updating/syntax/preterm.ma
index b7b90a4cf..6406d1dd7 100644
--- a/matita/matita/contribs/lambdadelta/delayed_updating/syntax/preterm.ma
+++ b/matita/matita/contribs/lambdadelta/delayed_updating/syntax/preterm.ma
@@ -27,3 +27,15 @@ definition structure_injective: predicate prototerm ≝
 interpretation
   "preterm (prototerm)"
   'ClassT = (structure_injective).
+
+(* Basic inversions *********************************************************)
+
+lemma preterm_in_root_append_inv_structure_empty_dx (t) (p) (q):
+      p●q ϵ ▵t → t ϵ 𝐓 → 𝐞 = ⊗q → 𝐞 = q.
+#t #p #q #Hpq #Ht #Hq
+lapply (Ht p ?? Hpq ?)
+[ <structure_append //
+| /2 width=2 by prototerm_in_root_append_des_sn/
+| /2 width=3 by eq_inv_list_append_dx_dx_refl/
+]
+qed-.