From mboxrd@z Thu Jan 1 00:00:00 1970 X-Msuck: nntp://news.gmane.io/gmane.science.mathematics.categories/6143 Path: news.gmane.org!not-for-mail From: pare@mathstat.dal.ca (Robert Pare) Newsgroups: gmane.science.mathematics.categories Subject: Canonical quotients Date: Sun, 12 Sep 2010 09:04:38 -0300 (ADT) Message-ID: <20100912120438.14DF55C186@chase.mathstat.dal.ca> Reply-To: pare@mathstat.dal.ca (Robert Pare) NNTP-Posting-Host: lo.gmane.org Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit X-Trace: dough.gmane.org 1284320908 4226 80.91.229.12 (12 Sep 2010 19:48:28 GMT) X-Complaints-To: usenet@dough.gmane.org NNTP-Posting-Date: Sun, 12 Sep 2010 19:48:28 +0000 (UTC) To: categories@mta.ca Original-X-From: majordomo@mlist.mta.ca Sun Sep 12 21:48:26 2010 Return-path: Envelope-to: gsmc-categories@m.gmane.org Original-Received: from smtpy.mta.ca ([138.73.1.139]) by lo.gmane.org with esmtp (Exim 4.69) (envelope-from ) id 1OusXI-00059k-3c for gsmc-categories@m.gmane.org; Sun, 12 Sep 2010 21:48:24 +0200 Original-Received: from mlist.mta.ca ([138.73.1.63]:55385) by smtpy.mta.ca with esmtp (Exim 4.71) (envelope-from ) id 1OusVh-0005Xm-0u; Sun, 12 Sep 2010 16:46:45 -0300 Original-Received: from majordomo by mlist.mta.ca with local (Exim 4.71) (envelope-from ) id 1OusVd-0001wQ-9G for categories-list@mlist.mta.ca; Sun, 12 Sep 2010 16:46:41 -0300 Precedence: bulk Xref: news.gmane.org gmane.science.mathematics.categories:6143 Archived-At: Peter Freyd's and John Kennison's examples definitively settled Mike Barr's question about canonical subobjects that compose. But I had started thinking about it and had what I thought would be a nice example. The category of sets has canonical quotients (equivalence classes) but they don't compose. I think there is no choice that do, but so far I haven't been able to prove or disprove this. Anybody? Bob [For admin and other information see: http://www.mta.ca/~cat-dist/ ]