X-Git-Url: http://matita.cs.unibo.it/gitweb/?a=blobdiff_plain;f=matita%2Fmatita%2Fcontribs%2Flambdadelta%2Fbasic_2%2Fstatic%2Flfxs.ma;h=9f0a1a4865522b6c685acbf242e721c207a2027a;hb=6d1c6a2cfdd1909647db5648b9cd059c61b19b40;hp=a1d50e69f243bd9c9ea175138630e9d3008e16df;hpb=c0a8f89161e9887c38eb5cf701f0f0c05a0e527f;p=helm.git

diff --git a/matita/matita/contribs/lambdadelta/basic_2/static/lfxs.ma b/matita/matita/contribs/lambdadelta/basic_2/static/lfxs.ma
index a1d50e69f..9f0a1a486 100644
--- a/matita/matita/contribs/lambdadelta/basic_2/static/lfxs.ma
+++ b/matita/matita/contribs/lambdadelta/basic_2/static/lfxs.ma
@@ -253,6 +253,13 @@ lemma lfxs_fwd_pair_sn: ∀R,I,L1,L2,V,T. L1 ⦻*[R, ②{I}V.T] L2 → L1 ⦻*[R
 #R * /2 width=4 by lfxs_fwd_flat_sn, lfxs_fwd_bind_sn/
 qed-.
 
+lemma lfxs_fwd_dx: ∀R,I,L1,K2,T,V2. L1 ⦻*[R, T] K2.ⓑ{I}V2 →
+                   ∃∃K1,V1. L1 = K1.ⓑ{I}V1.
+#R #I #L1 #K2 #T #V2 * #f elim (pn_split f) * #g #Hg #_ #Hf destruct
+[ elim (lexs_inv_push2 … Hf) | elim (lexs_inv_next2 … Hf) ] -Hf #K1 #V1 #_ #_ #H destruct
+/2 width=3 by ex1_2_intro/
+qed-.
+
 (* Basic_2A1: removed theorems 24:
               llpx_sn_sort llpx_sn_skip llpx_sn_lref llpx_sn_free llpx_sn_gref
               llpx_sn_bind llpx_sn_flat