explicit nonfix for union and inter

--- a/src/HOL/Library/ExecutableSet.thy	Thu Oct 12 22:57:45 2006 +0200
+++ b/src/HOL/Library/ExecutableSet.thy	Fri Oct 13 09:02:21 2006 +0200
@@ -230,6 +230,11 @@
 
 section {* code generator setup *}
 
+ML {*
+nonfix inter;
+nonfix union;
+*}
+
 code_constname
   "ExecutableSet.member" "List.member"
   "ExecutableSet.insertl" "List.insertl"