src/Pure/System/session.scala

--- a/src/Pure/System/session.scala	Sat Jul 02 20:54:38 2011 +0200
+++ b/src/Pure/System/session.scala	Sat Jul 02 21:24:19 2011 +0200
@@ -116,6 +116,8 @@
 
   /** main protocol actor **/
 
+  val thy_header = new Thy_Header(system.symbols)
+
   @volatile private var syntax = new Outer_Syntax(system.symbols)
   def current_syntax(): Outer_Syntax = syntax