X-Git-Url: http://matita.cs.unibo.it/gitweb/?p=helm.git;a=blobdiff_plain;f=matita%2Fmatita%2Fcontribs%2Flambdadelta%2Fstatic_2%2Frelocation%2Flifts.ma;h=060f3b8057d843e509201ed69a526d62895c6f01;hp=1d6225393ab9c483dee902e2184ac9fddd898fd5;hb=0d1dc967bc12041b9d23ee945db9dd91335e8c1d;hpb=df0dc72bccac82b3dd69108b5996d7008d007601

diff --git a/matita/matita/contribs/lambdadelta/static_2/relocation/lifts.ma b/matita/matita/contribs/lambdadelta/static_2/relocation/lifts.ma
index 1d6225393..060f3b805 100644
--- a/matita/matita/contribs/lambdadelta/static_2/relocation/lifts.ma
+++ b/matita/matita/contribs/lambdadelta/static_2/relocation/lifts.ma
@@ -56,6 +56,10 @@ definition deliftable2_bi: predicate (relation term) ≝
                            λR. ∀U1,U2. R U1 U2 → ∀f,T1. ⬆*[f] T1 ≘ U1 →
                            ∀T2. ⬆*[f] T2 ≘ U2 → R T1 T2.
 
+definition deliftable2_dx: predicate (relation term) ≝
+                           λR. ∀U1,U2. R U1 U2 → ∀f,T2. ⬆*[f] T2 ≘ U2 →
+                           ∃∃T1. ⬆*[f] T1 ≘ U1 & R T1 T2.
+
 (* Basic inversion lemmas ***************************************************)
 
 fact lifts_inv_sort1_aux: ∀f,X,Y. ⬆*[f] X ≘ Y → ∀s. X = ⋆s → Y = ⋆s.
@@ -329,6 +333,11 @@ qed-.
 
 (* Basic properties *********************************************************)
 
+lemma deliftable2_sn_dx (R): symmetric … R → deliftable2_sn R → deliftable2_dx R.
+#R #H2R #H1R #U1 #U2 #HU12 #f #T2 #HTU2
+elim (H1R … U1 … HTU2) -H1R /3 width=3 by ex2_intro/
+qed-.
+
 lemma lifts_eq_repl_back: ∀T1,T2. eq_repl_back … (λf. ⬆*[f] T1 ≘ T2).
 #T1 #T2 #f1 #H elim H -T1 -T2 -f1
 /4 width=5 by lifts_flat, lifts_bind, lifts_lref, at_eq_repl_back, eq_push/