diff -r 96942bf94a0c -r c7dd9d8c770a lemon/traits.h
--- a/lemon/traits.h	Mon Nov 14 18:35:20 2005 +0000
+++ b/lemon/traits.h	Mon Nov 14 18:36:45 2005 +0000
@@ -100,8 +100,8 @@
     typedef typename Map::Key Key;
     typedef typename Map::Value Value;
 
-    typedef Value ConstReturnValue;
-    typedef Value& ReturnValue;
+    typedef const Value ConstReturnValue;
+    typedef const Value ReturnValue;
   };
 
   template <typename Map>