>Here's an example.
(see Jim's message for the example)

Thanks, Jim. I understood. Indeed, as John said, I think that this case is actually alleviated -not complicated- with the use of surrogates. Indeed using surrogates adds flexibility to changing requirements. In my expirience, this is actually once of the most important advantages to surrogates, and probably the most important reason to ALWAYS use them, toghether with the advantages that any consistent method has.

Thanks again for the example. It was perfect.