--- a/ProgTutorial/output_tutorial.ML	Fri Oct 02 15:38:14 2009 +0200
+++ b/ProgTutorial/output_tutorial.ML	Sat Oct 03 13:01:39 2009 +0200
@@ -5,8 +5,8 @@
 (* rebuilding the output function from ThyOutput in order to *)
 (* enable the options [gray, linenos]                        *)
 
-val gray = ref false
-val linenos = ref false
+val gray = Unsynchronized.ref false
+val linenos = Unsynchronized.ref false
 
 
 fun output txt =