--- a/ProgTutorial/Helper/Command/Command.thy	Fri Oct 02 15:38:14 2009 +0200
+++ b/ProgTutorial/Helper/Command/Command.thy	Sat Oct 03 13:01:39 2009 +0200
@@ -40,7 +40,7 @@
 *}
 
 ML {*
-val r = ref (NONE:(unit -> term) option)
+val r = Unsynchronized.ref (NONE:(unit -> term) option)
 *}
 ML{*
 let