From mboxrd@z Thu Jan 1 00:00:00 1970 X-Msuck: nntp://news.gmane.io/gmane.science.mathematics.categories/8525 Path: news.gmane.org!not-for-mail From: Andrew Pitts Newsgroups: gmane.science.mathematics.categories Subject: Re: Category without objects Date: Thu, 5 Mar 2015 15:28:44 +0000 Message-ID: References: Reply-To: Andrew Pitts NNTP-Posting-Host: plane.gmane.org Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8 X-Trace: ger.gmane.org 1425580596 7276 80.91.229.3 (5 Mar 2015 18:36:36 GMT) X-Complaints-To: usenet@ger.gmane.org NNTP-Posting-Date: Thu, 5 Mar 2015 18:36:36 +0000 (UTC) Cc: categories@mta.ca, "Prof. Andrew M Pitts" To: Uwe Egbert Wolter Original-X-From: majordomo@mlist.mta.ca Thu Mar 05 19:36:28 2015 Return-path: Envelope-to: gsmc-categories@m.gmane.org Original-Received: from smtp3.mta.ca ([138.73.1.127]) by plane.gmane.org with esmtp (Exim 4.69) (envelope-from ) id 1YTadD-0000YB-R5 for gsmc-categories@m.gmane.org; Thu, 05 Mar 2015 19:36:24 +0100 Original-Received: from mlist.mta.ca ([138.73.1.63]:53266) by smtp3.mta.ca with esmtp (Exim 4.80) (envelope-from ) id 1YTac8-0003sZ-Cw; Thu, 05 Mar 2015 14:35:16 -0400 Original-Received: from majordomo by mlist.mta.ca with local (Exim 4.71) (envelope-from ) id 1YTac7-0007Y7-Mm for categories-list@mlist.mta.ca; Thu, 05 Mar 2015 14:35:15 -0400 In-Reply-To: Precedence: bulk Xref: news.gmane.org gmane.science.mathematics.categories:8525 Archived-At: [Note from moderator: Many responses to this; will forward the first mentioning each source. Thanks to other posters. ] On 5 March 2015 at 11:49, Uwe Egbert Wolter wrote: > Some years ago (around 30?) 25 > I read a book where it was mentioned that > one could define categories without (explicit) objects in the sense that > objects are mimicked by identity morphisms. Unfortunately, I can not > reconstruct what book it was. > > I know how this works. I would, however, like to have a reference. Peter J Freyd and Andre Scedrov, "Categories, Allegories" (Elsevier, 1990) ISBN 0 444 70368 3 is one such. Best wishes, Andy Pitts [For admin and other information see: http://www.mta.ca/~cat-dist/ ]