diff -r ff6b0c1087f2 -r 95f1e700b712 src/ZF/Coind/Values.thy
--- a/src/ZF/Coind/Values.thy	Tue Mar 06 16:06:52 2012 +0000
+++ b/src/ZF/Coind/Values.thy	Tue Mar 06 16:46:27 2012 +0000
@@ -80,7 +80,7 @@
 (* Equalities for value environments *)
 
 lemma ve_dom_owr [simp]:
-     "[| ve \<in> ValEnv; v \<noteq>0 |] ==> ve_dom(ve_owr(ve,x,v)) = ve_dom(ve) Un {x}"
+     "[| ve \<in> ValEnv; v \<noteq>0 |] ==> ve_dom(ve_owr(ve,x,v)) = ve_dom(ve) \<union> {x}"
 apply (erule ValEnvE)
 apply (auto simp add: map_domain_owr)
 done