diff -r e1bd8a54c40f -r d7728f65b353 src/HOL/Probability/Sigma_Algebra.thy
--- a/src/HOL/Probability/Sigma_Algebra.thy	Mon Sep 13 08:43:48 2010 +0200
+++ b/src/HOL/Probability/Sigma_Algebra.thy	Mon Sep 13 11:13:15 2010 +0200
@@ -716,7 +716,7 @@
 
 lemma range_binaryset_eq: "range(binaryset A B) = {A,B,{}}"
   apply (simp add: binaryset_def)
-  apply (rule set_ext)
+  apply (rule set_eqI)
   apply (auto simp add: image_iff)
   done