--- a/ProgTutorial/Intro.thy	Tue Nov 17 20:36:18 2009 +0100
+++ b/ProgTutorial/Intro.thy	Tue Nov 17 23:59:19 2009 +0100
@@ -228,7 +228,7 @@
   are by him.
 
   \item {\bf Lukas Bulwahn} made me aware of the problems with recursive
-  parsers.
+  parsers and contributed exercise \ref{ex:contextfree}.
 
   \item {\bf Jeremy Dawson} wrote the first version of the chapter
   about parsing.