--- a/doc-src/TutorialI/Misc/Option2.thy Mon May 02 10:56:13 2005 +0200
+++ b/doc-src/TutorialI/Misc/Option2.thy Mon May 02 11:03:27 2005 +0200
@@ -14,7 +14,7 @@
text{*\noindent
Frequently one needs to add a distinguished element to some existing type.
For example, type @{text"t option"} can model the result of a computation that
-may either terminate with an error (represented by @{term None}) or return
+may either terminate with an error (represented by @{const None}) or return
some value @{term v} (represented by @{term"Some v"}).
Similarly, @{typ nat} extended with $\infty$ can be modeled by type
@{typ"nat option"}. In both cases one could define a new datatype with