From mboxrd@z Thu Jan 1 00:00:00 1970 X-Msuck: nntp://news.gmane.io/gmane.science.mathematics.categories/9336 Path: news.gmane.org!.POSTED!not-for-mail From: John Baez Newsgroups: gmane.science.mathematics.categories Subject: Re: Fred Date: Sat, 9 Sep 2017 09:15:17 +0800 Message-ID: References: Reply-To: John Baez 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 1505137739 3283 195.159.176.226 (11 Sep 2017 13:48:59 GMT) X-Complaints-To: usenet@blaine.gmane.org NNTP-Posting-Date: Mon, 11 Sep 2017 13:48:59 +0000 (UTC) To: categories Original-X-From: majordomo@mlist.mta.ca Mon Sep 11 15:48:51 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 1drP4v-00009p-IW for gsmc-categories@m.gmane.org; Mon, 11 Sep 2017 15:48:45 +0200 Original-Received: from mlist.mta.ca ([138.73.1.63]:38324) by smtp2.mta.ca with esmtp (Exim 4.80) (envelope-from ) id 1drP5K-0006QV-9f; Mon, 11 Sep 2017 10:49:10 -0300 Original-Received: from majordomo by mlist.mta.ca with local (Exim 4.71) (envelope-from ) id 1drP3e-0004Pt-Qo for categories-list@mlist.mta.ca; Mon, 11 Sep 2017 10:47:26 -0300 In-Reply-To: Precedence: bulk Xref: news.gmane.org gmane.science.mathematics.categories:9336 Archived-At: Dear Categorists - Vaughan wrote: >> There is one other anecdote about UACT, nothing to do with Fred, that I >> have always loved. In the course of MSRI director Bill Thurston' >> opening remarks, he said words to the effect that the notion of the >> opposite of a category made him nauseous. This was the only meeting I >> have ever attended where fully half the attendees drew in enough breath >> to drop the air pressure by an audible amount. Since "nauseous" means "causing nausea", perhaps Thurston's remark had just sickened the audience. Emily wrote: > I=E2=80=99ll confess that the idea of an opposite category appearing as t= he > codomain of a functor also makes me somewhat nauseated (the > domain of course is no problem). Now here is someone well-attuned to these subtleties of English! I've always been delighted by opposite categories. Sometimes I think we live in one. For example: if you flip forward in a book you eventually reach the back, but if you go back far enough you reach the foreword... and in the ancient past everything was younger. I always tell my students that since category theory reduces all of mathematics to the study of arrows, and the only mistake you can make with an arrow is to get confused about which way it's pointing, they should expect to spend many hours confused about exactly this. Best, jb [For admin and other information see: http://www.mta.ca/~cat-dist/ ]