- some work on append

[helm.git] / matita / matita / contribs / lambdadelta / basic_2 / multiple / llor_ldrop.ma

diff --git a/matita/matita/contribs/lambdadelta/basic_2/multiple/llor_ldrop.ma b/matita/matita/contribs/lambdadelta/basic_2/multiple/llor_ldrop.ma
index b766269e7ded295a859dd85500d3f722224ae256..f247442917f0a76e15a187fd94cbd78d7881926e 100644 (file)
--- a/matita/matita/contribs/lambdadelta/basic_2/multiple/llor_ldrop.ma
+++ b/matita/matita/contribs/lambdadelta/basic_2/multiple/llor_ldrop.ma
@@ -19,4 +19,12 @@ include "basic_2/multiple/llor.ma".
 
 (* Advanced properties ******************************************************)
 
+lemma llor_skip: ∀L1,L2,U,d. |L1| ≤ |L2| → yinj (|L1|) ≤ d → L1 ⩖[U, d] L2 ≡ L1.
+#L1 #L2 #U #d #HL12 #Hd @and3_intro // -HL12
+#I1 #I2 #I #K1 #K2 #K #W1 #W2 #W #i #HLK1 #_ #HLK -I2 -L2 -K2
+lapply (ldrop_mono … HLK … HLK1) -HLK #H destruct
+lapply (ldrop_fwd_length_lt2 … HLK1) -K1
+/5 width=3 by ylt_yle_trans, ylt_inj, or3_intro0, and3_intro/
+qed.
+
 axiom llor_total: ∀L1,L2,T,d. |L1| ≤ |L2| → ∃L. L1 ⩖[T, d] L2 ≡ L.