X-Git-Url: http://matita.cs.unibo.it/gitweb/?p=helm.git;a=blobdiff_plain;f=matita%2Fmatita%2Fcontribs%2Flambdadelta%2Fdelayed_updating%2Freduction%2Fibfr.ma;h=90b16d3de1941cf62d8bd2fcee61aa8133df92b0;hp=869ad57545a013356c1649f749ad933c9e740b78;hb=513c4a61f11ce03888a8a0f9d8e513de6e3a7c8b;hpb=48cd63fc7f4415925582eae224a36a9c1bb3cc06

diff --git a/matita/matita/contribs/lambdadelta/delayed_updating/reduction/ibfr.ma b/matita/matita/contribs/lambdadelta/delayed_updating/reduction/ibfr.ma
index 869ad5754..90b16d3de 100644
--- a/matita/matita/contribs/lambdadelta/delayed_updating/reduction/ibfr.ma
+++ b/matita/matita/contribs/lambdadelta/delayed_updating/reduction/ibfr.ma
@@ -35,3 +35,12 @@ definition ibfr (r): relation2 prototerm prototerm ≝
 interpretation
   "balanced focused reduction with immediate updating (prototerm)"
   'BlackRightArrowIBF t1 r t2 = (ibfr r t1 t2).
+
+(* Constructions with subset_equivalence ************************************)
+
+lemma ibfr_eq_trans (t) (t1) (t2) (r):
+      t1 ➡𝐢𝐛𝐟[r] t → t ⇔ t2 → t1 ➡𝐢𝐛𝐟[r] t2.
+#t #t1 #t2 #r
+* #p #b #q #m #n #Hr #Hb #Hm #Hn #Ht1 #Ht #Ht2
+/3 width=13 by subset_eq_trans, ex6_5_intro/
+qed-.