From mboxrd@z Thu Jan 1 00:00:00 1970 X-Msuck: nntp://news.gmane.io/gmane.science.mathematics.categories/8526 Path: news.gmane.org!not-for-mail From: Jiri Adamek Newsgroups: gmane.science.mathematics.categories Subject: Re: Category without objects Date: Thu, 5 Mar 2015 17:49:53 +0100 (CET) Message-ID: References: Reply-To: Jiri Adamek NNTP-Posting-Host: plane.gmane.org Mime-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII; format=flowed X-Trace: ger.gmane.org 1425580735 9757 80.91.229.3 (5 Mar 2015 18:38:55 GMT) X-Complaints-To: usenet@ger.gmane.org NNTP-Posting-Date: Thu, 5 Mar 2015 18:38:55 +0000 (UTC) Cc: categories@mta.ca To: Uwe Egbert Wolter Original-X-From: majordomo@mlist.mta.ca Thu Mar 05 19:38:40 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 1YTafL-0002K8-23 for gsmc-categories@m.gmane.org; Thu, 05 Mar 2015 19:38:35 +0100 Original-Received: from mlist.mta.ca ([138.73.1.63]:53278) by smtp3.mta.ca with esmtp (Exim 4.80) (envelope-from ) id 1YTaep-0004Cn-2V; Thu, 05 Mar 2015 14:38:03 -0400 Original-Received: from majordomo by mlist.mta.ca with local (Exim 4.71) (envelope-from ) id 1YTaen-0007eC-Py for categories-list@mlist.mta.ca; Thu, 05 Mar 2015 14:38:01 -0400 Precedence: bulk Xref: news.gmane.org gmane.science.mathematics.categories:8526 Archived-At: See Definition 3.8 in Herrlich & Strecker: Category Theory (42 years old...). Cheers Jiri xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx alternative e-mail address (in case reply key does not work): J.Adamek@tu-bs.de xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx On Thu, 5 Mar 2015, Uwe Egbert Wolter wrote: > Some years ago (around 30?) 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. > > Best > > Uwe Wolter > [For admin and other information see: http://www.mta.ca/~cat-dist/ ]