From mboxrd@z Thu Jan 1 00:00:00 1970 X-Msuck: nntp://news.gmane.io/gmane.science.mathematics.categories/7020 Path: news.gmane.org!not-for-mail From: David Leduc Newsgroups: gmane.science.mathematics.categories Subject: Dualizing comma categories Date: Sun, 30 Oct 2011 12:34:59 +0000 Message-ID: Reply-To: David Leduc NNTP-Posting-Host: lo.gmane.org Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 X-Trace: dough.gmane.org 1319982214 10248 80.91.229.12 (30 Oct 2011 13:43:34 GMT) X-Complaints-To: usenet@dough.gmane.org NNTP-Posting-Date: Sun, 30 Oct 2011 13:43:34 +0000 (UTC) To: categories Original-X-From: majordomo@mlist.mta.ca Sun Oct 30 14:43:30 2011 Return-path: Envelope-to: gsmc-categories@m.gmane.org Original-Received: from smtpx.mta.ca ([138.73.1.4]) by lo.gmane.org with esmtp (Exim 4.69) (envelope-from ) id 1RKVfd-0005Rn-Gg for gsmc-categories@m.gmane.org; Sun, 30 Oct 2011 14:43:29 +0100 Original-Received: from mlist.mta.ca ([138.73.1.63]:39073) by smtpx.mta.ca with esmtp (Exim 4.76) (envelope-from ) id 1RKVbw-0006yu-VF; Sun, 30 Oct 2011 10:39:40 -0300 Original-Received: from majordomo by mlist.mta.ca with local (Exim 4.71) (envelope-from ) id 1RKVbv-0005yH-G5 for categories-list@mlist.mta.ca; Sun, 30 Oct 2011 10:39:39 -0300 Precedence: bulk Xref: news.gmane.org gmane.science.mathematics.categories:7020 Archived-At: Hi, A comma category is a comma object in the 2-category Cat of categories and functors. And a comma object is defined by a universal property. Now, one can dualize the notion of comma object by turning around the 1-cells and/or 2-cells in its definition. My question is: when we instantiate those dualized definitions to Cat, what do we obtain? In other words, what is a "co-comma category"? For example, since the product of two categories is a special case of comma category, I would expect that the coproduct of two categories is a special case of "co-comma category". Thanks! [For admin and other information see: http://www.mta.ca/~cat-dist/ ]