From mboxrd@z Thu Jan 1 00:00:00 1970 X-Msuck: nntp://news.gmane.io/gmane.science.mathematics.categories/4548 Path: news.gmane.org!not-for-mail From: Dana Scott Newsgroups: gmane.science.mathematics.categories Subject: Re: Categories and functors, query Date: Sun, 7 Sep 2008 18:25:39 -0700 Message-ID: NNTP-Posting-Host: main.gmane.org Mime-Version: 1.0 (Apple Message framework v926) Content-Type: text/plain; charset=US-ASCII; format=flowed; delsp=yes Content-Transfer-Encoding: 7bit X-Trace: ger.gmane.org 1241020019 13796 80.91.229.2 (29 Apr 2009 15:46:59 GMT) X-Complaints-To: usenet@ger.gmane.org NNTP-Posting-Date: Wed, 29 Apr 2009 15:46:59 +0000 (UTC) To: categories@mta.ca Original-X-From: rrosebru@mta.ca Mon Sep 8 08:02:57 2008 -0300 Return-path: Envelope-to: categories-list@mta.ca Delivery-date: Mon, 08 Sep 2008 08:02:57 -0300 Original-Received: from Majordom by mailserv.mta.ca with local (Exim 4.61) (envelope-from ) id 1KceRD-0006t5-Hr for categories-list@mta.ca; Mon, 08 Sep 2008 07:57:43 -0300 Original-Sender: cat-dist@mta.ca Precedence: bulk X-Keywords: X-UID: 16 Original-Lines: 24 Xref: news.gmane.org gmane.science.mathematics.categories:4548 Archived-At: On Sep 7, 2008, at 2:33 PM, R Brown wrote: > There is another curiosity about the axioms for a category, namely the > infuence of the known axioms for a groupoid (Brandt, 1926). Bill > Cockcroft > told me that these axioms had influenced E-M. These axioms were well > used in > the algebra group at Chicago. However when I asked Sammy about this > in 1985 > he firmly said `no, and was why the notion of groupoid did not > appear as an > example in the E-M paper'! > > Perhaps it was a case of forgetting the influence? I certainly heard Saunders mention Brandt groupoids as examples. (Not very good examples, since all maps are invertible.) But, as everyone knows, it is not the definition of a category that is the key part, but seeing that functors and natural transformations are interesting.