tuned comment

--- a/src/HOL/Library/Executable_Set.thy	Fri Jun 10 17:52:09 2011 +0200
+++ b/src/HOL/Library/Executable_Set.thy	Sat Jun 11 07:50:28 2011 +0200
@@ -12,7 +12,7 @@
 text {*
   This is just an ad-hoc hack which will rarely give you what you want.
   For the moment, whenever you need executable sets, consider using
-  type @{text fset} from theory @{text Cset}.
+  type @{text Cset.set} from theory @{text Cset}.
 *}
 
 declare mem_def [code del]