--- a/src/core/ptr.h	Mon Oct 08 10:28:52 2007 +0200
+++ b/src/core/ptr.h	Fri Oct 05 19:13:36 2007 +0100
@@ -352,6 +352,11 @@
   return PeekPointer (lhs) != PeekPointer (rhs);
 }
 
+template <typename T>
+bool operator < (Ptr<T> const &lhs, Ptr<T> const &rhs)
+{
+  return PeekPointer<T> (lhs) < PeekPointer<T> (rhs);
+}
 
 template <typename T1, typename T2>
 Ptr<T1>