diff -r b4f1a0a701ae -r 410115884a92 src/Doc/Isar_Ref/Preface.thy
--- a/src/Doc/Isar_Ref/Preface.thy	Sat May 16 12:05:52 2015 +0200
+++ b/src/Doc/Isar_Ref/Preface.thy	Sun May 17 21:44:34 2015 +0200
@@ -2,8 +2,6 @@
 imports Base Main
 begin
 
-chapter \<open>Preface\<close>
-
 text \<open>
   The \emph{Isabelle} system essentially provides a generic
   infrastructure for building deductive systems (programmed in