I already have some minor revisions to make to my report on sketches that I have made available by ftp. 1) The paper is available in the directory math/wells on ftp.cwru.edu. (I omitted the "math" part.) 2) Add this citation to line 12 of page 12: "Geometric Logic in Computer Science", by Steve Vickers. Available by FTP from theory.doc.ic.ac.uk in directory papers/Vickers. The paper is called GLiCS.dvi. 3) (Important) The discussion in the middle of page 12 concerning conceptual completeness is badly worded. ("Badly worded" means "wrong".) Besides that, it belongs in the section on categorial model theory. It should read In connection with this, one can ask whether, for a particular type of theory, a morphism of theories that induces an equivalence on the category of models must be an equivalence of theories (conceptual completeness). The answer is yes for pretoposes [Makkai and Reyes, 1977], Chapter 8 (see also [Pitts, 1989]). Some form of Morita theory can also explain when categories of models are equivalent (but in this case without necessarily being induced by a morphism of theories); for this, see [references as given in paper]. -- Charles Wells Department of Mathematics Case Western Reserve University +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++