diff -r 1248d23d6e93 -r 8af504c71ac4 lemon/bits/graph_adaptor_extender.h
--- a/lemon/bits/graph_adaptor_extender.h	Wed Mar 17 10:23:17 2010 +0100
+++ b/lemon/bits/graph_adaptor_extender.h	Tue Apr 06 06:43:04 2010 +0200
@@ -181,6 +181,8 @@
     typedef _Graph Graph;
     typedef GraphAdaptorExtender Adaptor;
 
+    typedef True UndirectedTag;
+
     typedef typename Parent::Node Node;
     typedef typename Parent::Arc Arc;
     typedef typename Parent::Edge Edge;