src/Pure/System/isabelle_process.scala

--- a/src/Pure/System/isabelle_process.scala	Tue Sep 06 10:27:04 2011 +0200
+++ b/src/Pure/System/isabelle_process.scala	Tue Sep 06 11:18:19 2011 +0200
@@ -33,7 +33,7 @@
       ('H' : Int) -> Markup.RAW)
   }
 
-  abstract class Message
+  sealed abstract class Message
 
   class Input(name: String, args: List[String]) extends Message
   {