Mike Barr's post was transmitted badly, he offers to send a pdf to anyone interested. His address is: Michael Barr <barr@math.mcgill.ca> This is also an opportunity for me to remind you of the list policy from the list web page at: http://www.mta.ca/~cat-dist/ "The subject of this moderated mailing list is category theory. Items on another subject may be posted if judged by the moderator to be of interest to subscribers. Discussion of such posts is excluded. The list is to be used for concise discussion that is suitable for email distribution. Posts are not transmitted if, in the moderator's judgement, they are unsuitable for distribution. Postings to the categories list will be courteous and respectful. Expression of disagreement must be polite. A submission judged by the moderator to be offensive or defamatory will not be posted. Submissions judged to be related such material will not be posted. The categories mailing list distributes only text messages. Do not send attachments, messages containing html or excessively long postings (longer than about 10K). The default setting for some email clients is to compose messages containing html. This setting is easy to change. Postings with attachments or with html will be discarded." Best to all for 2016, Bob Rosebrugh [For admin and other information see: http://www.mta.ca/~cat-dist/ ]