Thomas, tf> ... Do^; (* re-uses the previous definition of Do in the "super object class" (A in this case) and is called a supercall *) ... OK, thanks. This structure of a module containing objects with associated methods appears to be very similar to the mathematical category containing objects and maps. So an AO module might be viewed as an instance of a category. Probably this aspect has been discussed in the literature. Anyone know of a specific publication? Thanks, ... Peter E. Desktops.OpenDoc http://carnot.pathology.ubc.ca/