diff -r 1d4a46f1fced -r 21693b7c8fbf src/Doc/IsarRef/Proof.thy
--- a/src/Doc/IsarRef/Proof.thy	Tue Sep 03 11:55:59 2013 +0200
+++ b/src/Doc/IsarRef/Proof.thy	Tue Sep 03 11:58:34 2013 +0200
@@ -1195,7 +1195,7 @@
   later.
 
   @{rail "
-    @@{command case} (caseref | '(' caseref (('_' | @{syntax name}) +) ')')
+    @@{command case} (caseref | '(' caseref (('_' | @{syntax name}) *) ')')
     ;
     caseref: nameref attributes?
     ;