diff -r 1d467e7ed320 -r 77704bf2a4ae lemon/bits/edge_set_extender.h
--- a/lemon/bits/edge_set_extender.h	Fri Mar 19 09:15:57 2010 +0100
+++ b/lemon/bits/edge_set_extender.h	Tue Apr 06 06:52:48 2010 +0200
@@ -280,6 +280,8 @@
 
     typedef EdgeSetExtender Graph;
 
+    typedef True UndirectedTag;
+
     typedef typename Parent::Node Node;
     typedef typename Parent::Arc Arc;
     typedef typename Parent::Edge Edge;