X-Git-Url: http://matita.cs.unibo.it/gitweb/?a=blobdiff_plain;f=matita%2Fmatita%2Fcontribs%2Flambda_delta%2FBasic_2%2Funfold%2Fldrops.ma;h=896415581910b592d23bf0e5875c5a23df1b2399;hb=7e6643f9ce7ae87e9241aeac5b6d828e9d47fb63;hp=c6bb67e79a8ca3d6d361155ca9f21d4d3ec79682;hpb=2fef56731b0d38913967105495b96754e327efab;p=helm.git

diff --git a/matita/matita/contribs/lambda_delta/Basic_2/unfold/ldrops.ma b/matita/matita/contribs/lambda_delta/Basic_2/unfold/ldrops.ma
index c6bb67e79..896415581 100644
--- a/matita/matita/contribs/lambda_delta/Basic_2/unfold/ldrops.ma
+++ b/matita/matita/contribs/lambda_delta/Basic_2/unfold/ldrops.ma
@@ -20,8 +20,20 @@ include "Basic_2/unfold/lifts.ma".
 inductive ldrops: list2 nat nat → relation lenv ≝
 | ldrops_nil : ∀L. ldrops ⟠ L L
 | ldrops_cons: ∀L1,L,L2,des,d,e.
-               ⇓[d,e] L1 ≡ L → ldrops des L L2 → ldrops ({d, e} :: des) L1 L2
+               ldrops des L1 L → ⇓[d,e] L ≡ L2 → ldrops ({d, e} :: des) L1 L2
 .
 
 interpretation "generic local environment slicing"
-   'RDrop des T1 T2 = (ldrops des T1 T2).
+   'RLDrop des T1 T2 = (ldrops des T1 T2).
+
+(* Basic properties *********************************************************)
+
+lemma ldrops_skip: ∀L1,L2,des. ⇓[des] L1 ≡ L2 → ∀V1,V2. ⇑[des] V2 ≡ V1 →
+                   ∀I. ⇓[ss des] L1. 𝕓{I} V1 ≡ L2. 𝕓{I} V2.
+#L1 #L2 #des #H elim H -L1 -L2 -des
+[ #L #V1 #V2 #HV12 #I
+  >(lifts_inv_nil … HV12) -HV12 //
+| #L1 #L #L2 #des #d #e #_ #HL2 #IHL #V1 #V2 #H #I
+  elim (lifts_inv_cons … H) -H /3 width=5/
+].
+qed.