diff -r 93dcfcf91484 -r 5130dfe1b7be src/Pure/Thy/thy_header.scala
--- a/src/Pure/Thy/thy_header.scala	Wed Jul 06 23:11:59 2011 +0200
+++ b/src/Pure/Thy/thy_header.scala	Thu Jul 07 13:48:30 2011 +0200
@@ -75,7 +75,7 @@
 
   def read(reader: Reader[Char]): Header =
   {
-    val token = lexicon.token(Isabelle_System.symbols, _ => false)
+    val token = lexicon.token(_ => false)
     val toks = new mutable.ListBuffer[Token]
 
     @tailrec def scan_to_begin(in: Reader[Char])