What then is a personal computer? One would hope that it would be both a medium for containing and expressing arbitrary symbolic notions, and also a collection of useful tools for manipulating these structures, with ways to add new tools to the repertoire. Another rarely invoked constraint is that it be superior to books and printing in at least some ways without being markedly inferior in others. (The previous remark seems to disallow known commercial display devices from consideration.) "Personal" also means owned by its user (needs to cost no more than a TV) and portable (which to me means that the user can easily carry the device and other things at the same time. Need we add that it be usable in the woods?