diff -r 3c8801529a1f -r 5d48b6773b73 src/include/invalid.h
--- a/src/include/invalid.h	Mon Apr 26 10:35:36 2004 +0000
+++ b/src/include/invalid.h	Mon Apr 26 11:11:55 2004 +0000
@@ -12,7 +12,12 @@
   
   /// See \ref INVALID, how to use it.
   
-  struct Invalid {};
+  struct Invalid {
+  public:
+    bool operator==(Invalid) { return true;  }
+    bool operator!=(Invalid) { return false; }
+    bool operator< (Invalid) { return false; }
+  };
   
   /// Invalid iterators.