From mboxrd@z Thu Jan 1 00:00:00 1970 X-Msuck: nntp://news.gmane.io/gmane.science.mathematics.categories/9419 Path: news.gmane.org!.POSTED!not-for-mail From: Michael Shulman Newsgroups: gmane.science.mathematics.categories Subject: Re: Some questions about different notions of "theory" Date: Thu, 9 Nov 2017 16:04:42 -0800 Message-ID: References: Reply-To: Michael Shulman NNTP-Posting-Host: blaine.gmane.org Mime-Version: 1.0 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Trace: blaine.gmane.org 1510356564 3412 195.159.176.226 (10 Nov 2017 23:29:24 GMT) X-Complaints-To: usenet@blaine.gmane.org NNTP-Posting-Date: Fri, 10 Nov 2017 23:29:24 +0000 (UTC) Cc: Mike Stay , categories To: =?UTF-8?Q?Andr=C3=A9e_Ehresmann?= Original-X-From: majordomo@mlist.mta.ca Sat Nov 11 00:29:20 2017 Return-path: Envelope-to: gsmc-categories@m.gmane.org Original-Received: from smtp2.mta.ca ([198.164.44.40]) by blaine.gmane.org with esmtp (Exim 4.84_2) (envelope-from ) id 1eDIjd-0000YT-BA for gsmc-categories@m.gmane.org; Sat, 11 Nov 2017 00:29:17 +0100 Original-Received: from mlist.mta.ca ([138.73.1.63]:59660) by smtp2.mta.ca with esmtp (Exim 4.80) (envelope-from ) id 1eDIk4-0004IB-OJ; Fri, 10 Nov 2017 19:29:44 -0400 Original-Received: from majordomo by mlist.mta.ca with local (Exim 4.71) (envelope-from ) id 1eDIid-00007o-ND for categories-list@mlist.mta.ca; Fri, 10 Nov 2017 19:28:15 -0400 In-Reply-To: Precedence: bulk Xref: news.gmane.org gmane.science.mathematics.categories:9419 Archived-At: On Thu, Nov 9, 2017 at 3:26 AM, Andr=C3=A9e Ehresmann wrote: > I have been > surprised to see the definition given in nLab of a sketch as a category > with some limit-cones and co-limit-cones. For us, a 'sketch' is a > category S (or even a graph) with some distinguished cones and co-cones > (but not necessarily (co-)limit-cones). Thanks for pointing this out. I think this is an error on the nLab page, or perhaps a sloppy phrasing that got misinterpreted by a later editor; I'll fix it. In the case when a sketch is a graph rather than a category, it has to come equipped also with some distinguished diagrams that are supposed to commute in its models, right? [For admin and other information see: http://www.mta.ca/~cat-dist/ ]