From mboxrd@z Thu Jan 1 00:00:00 1970 X-Msuck: nntp://news.gmane.io/gmane.science.mathematics.categories/6194 Path: news.gmane.org!not-for-mail From: David Yetter Newsgroups: gmane.science.mathematics.categories Subject: Re: are fibrations evil? Date: Sun, 19 Sep 2010 09:57:24 -0500 Message-ID: References: Reply-To: David Yetter NNTP-Posting-Host: lo.gmane.org Mime-Version: 1.0 (Apple Message framework v1081) Content-Type: text/plain; charset=iso-8859-1 Content-Transfer-Encoding: quoted-printable X-Trace: dough.gmane.org 1284998373 15489 80.91.229.12 (20 Sep 2010 15:59:33 GMT) X-Complaints-To: usenet@dough.gmane.org NNTP-Posting-Date: Mon, 20 Sep 2010 15:59:33 +0000 (UTC) Cc: "John Baez" , "categories" To: =?iso-8859-1?Q?Andr=E9?= Original-X-From: majordomo@mlist.mta.ca Mon Sep 20 17:59:31 2010 Return-path: Envelope-to: gsmc-categories@m.gmane.org Original-Received: from smtpy.mta.ca ([138.73.1.139]) by lo.gmane.org with esmtp (Exim 4.69) (envelope-from ) id 1OximB-00005l-00 for gsmc-categories@m.gmane.org; Mon, 20 Sep 2010 17:59:31 +0200 Original-Received: from mlist.mta.ca ([138.73.1.63]:46350) by smtpy.mta.ca with esmtp (Exim 4.71) (envelope-from ) id 1Oxiky-000069-8q; Mon, 20 Sep 2010 12:58:17 -0300 Original-Received: from majordomo by mlist.mta.ca with local (Exim 4.71) (envelope-from ) id 1Oxikp-0005Lp-4A for categories-list@mlist.mta.ca; Mon, 20 Sep 2010 12:58:07 -0300 In-Reply-To: Precedence: bulk Xref: news.gmane.org gmane.science.mathematics.categories:6194 Archived-At: Dear Andre: Brevity is the usual reason for introducing new terminology. And, ultimately there is a need, as mathematics would grind to a halt if one had to write out a phrase giving the content of each concept whenever one wanted to talk about it. One may object to the jocular use of a word with a moral denotation as the name for a mathematical concept, but four=20 characters beats 28 characters (or 31 if one counts spaces). It certainly seems desirable to have a brief name for either "invariant under equivalence" or "not invariant under=20 equivalence". Best Thoughts, David Y. On 18 Sep 2010, at 08:50, Joyal, Andr=E9 wrote: > Dear John, >=20 > A property is "evil" in your sense if it is > not invariant under equivalences. > Invariance under equivalence is a well > established mathematical notion. > I prefer to say that something is not > invariant under equivalence than to say > that it is "evil". There is no need to > introduce a new terminology. >=20 > Best, > Andr=E9=20 >=20 [For admin and other information see: http://www.mta.ca/~cat-dist/ ]