From mboxrd@z Thu Jan 1 00:00:00 1970 X-Msuck: nntp://news.gmane.io/gmane.science.mathematics.categories/7382 Path: news.gmane.org!not-for-mail From: Andrej Bauer Newsgroups: gmane.science.mathematics.categories Subject: Re: regular monos of groups Date: Sun, 15 Jul 2012 23:27:15 +0200 Message-ID: References: Reply-To: Andrej Bauer NNTP-Posting-Host: plane.gmane.org Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8 X-Trace: dough.gmane.org 1342423746 19813 80.91.229.3 (16 Jul 2012 07:29:06 GMT) X-Complaints-To: usenet@dough.gmane.org NNTP-Posting-Date: Mon, 16 Jul 2012 07:29:06 +0000 (UTC) To: categories@mta.ca Original-X-From: majordomo@mlist.mta.ca Mon Jul 16 09:29:06 2012 Return-path: Envelope-to: gsmc-categories@m.gmane.org Original-Received: from smtpx.mta.ca ([138.73.1.80]) by plane.gmane.org with esmtp (Exim 4.69) (envelope-from ) id 1Sqfjs-0004me-8I for gsmc-categories@m.gmane.org; Mon, 16 Jul 2012 09:29:04 +0200 Original-Received: from mlist.mta.ca ([138.73.1.63]:56756) by smtpx.mta.ca with esmtp (Exim 4.77) (envelope-from ) id 1Sqfiw-0004Sw-9w; Mon, 16 Jul 2012 04:28:06 -0300 Original-Received: from majordomo by mlist.mta.ca with local (Exim 4.71) (envelope-from ) id 1Sqfiv-0005eq-FH for categories-list@mlist.mta.ca; Mon, 16 Jul 2012 04:28:05 -0300 In-Reply-To: Precedence: bulk Xref: news.gmane.org gmane.science.mathematics.categories:7382 Archived-At: My blog post has a hole. I am not convinced by Paul's answer on Mathoverflow (perhaps I just have to work out the details which Paul left out). So this leaves the question: is every mono in the category of groups regular, constructively speaking? With kind regards, Andrej On Fri, Jun 22, 2012 at 9:19 AM, Paul Taylor wrote: > Mike Barr said > >> Somewhere I have seen a proof that all monics in the category of groups >> are regular. > > Somebody asked this question a while back on MathOverflow > and I gave the following proof, which is both constructive and > more explicit than the replies that have been given here. > > http://mathoverflow.net/questions/41208/are-all-group-monomorphisms-regular-constructively/46054#46054 > > Paul Taylor > [For admin and other information see: http://www.mta.ca/~cat-dist/ ]