diff -r e2c0d8ef29cb -r c399ae4b836f src/ZF/Arith.thy
--- a/src/ZF/Arith.thy	Sun Nov 02 16:09:35 2014 +0100
+++ b/src/ZF/Arith.thy	Sun Nov 02 16:39:54 2014 +0100
@@ -9,7 +9,7 @@
   Also, rec(m, 0, %z w.z) is pred(m).
 *)
 
-header{*Arithmetic Operators and Their Definitions*}
+section{*Arithmetic Operators and Their Definitions*}
 
 theory Arith imports Univ begin