diff -r cc6768509ed3 -r 33137422d7fd doc-src/IsarAdvanced/Codegen/Thy/examples/class.ML
--- a/doc-src/IsarAdvanced/Codegen/Thy/examples/class.ML	Tue Sep 18 08:28:47 2007 +0200
+++ b/doc-src/IsarAdvanced/Codegen/Thy/examples/class.ML	Tue Sep 18 10:44:02 2007 +0200
@@ -14,7 +14,7 @@
 fun head B_ (x :: xs) = x
   | head B_ [] = null B_;
 
-fun null_option () = {null = NONE} : ('b option) null;
+fun null_option () = {null = NONE} : ('a option) null;
 
 val dummy : Nat.nat option =
   head (null_option ()) [SOME (Nat.Suc Nat.Zero_nat), NONE];