I think we've been through this before, on another forum, and I do not want to sound overly polemical or partisan, but I do want to put in my two-cents worth (or whatever currency is appropriate wherever you are reading this). While I like what Goguen and Meseguer have done, separately and in collaboration, I think there are many important aspects of object-oriented programming that their work does not address. This is true of my work as well, although I think for different reasons. I believe that there are aspects of object-oriented programming that are important to programming practicianers (the kind that go to object-oriented programming conferences, not the ones with big DARPA contracts) that have not been adequately characterized in a mathematical way by any of us. For those interested in applying their favorite mathematical theory to a practical (and relatively abstract) problem, I would advocate attempting to formalize aspects of object-oriented programming. Did I offend anyone? I hope not. I just don't think the answers are in yet. John Mitchell ==============================================================================