From mboxrd@z Thu Jan 1 00:00:00 1970 X-Msuck: nntp://news.gmane.io/gmane.science.mathematics.categories/5822 Path: news.gmane.org!not-for-mail From: Michael Barr Newsgroups: gmane.science.mathematics.categories Subject: Re: "injective" terminology Date: Wed, 19 May 2010 05:59:15 -0400 (EDT) Message-ID: References: Reply-To: Michael Barr NNTP-Posting-Host: lo.gmane.org Mime-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII; format=flowed X-Trace: dough.gmane.org 1274315050 2937 80.91.229.12 (20 May 2010 00:24:10 GMT) X-Complaints-To: usenet@dough.gmane.org NNTP-Posting-Date: Thu, 20 May 2010 00:24:10 +0000 (UTC) To: "Prof. Peter Johnstone" Original-X-From: categories@mta.ca Thu May 20 02:24:08 2010 connect(): No such file or directory Return-path: Envelope-to: gsmc-categories@m.gmane.org Original-Received: from mailserv.mta.ca ([138.73.1.1]) by lo.gmane.org with esmtp (Exim 4.69) (envelope-from ) id 1OEtYW-0008Ts-9k for gsmc-categories@m.gmane.org; Thu, 20 May 2010 02:24:08 +0200 Original-Received: from Majordom by mailserv.mta.ca with local (Exim 4.61) (envelope-from ) id 1OEt7Z-00070j-Vs for categories-list@mta.ca; Wed, 19 May 2010 20:56:18 -0300 In-Reply-To: Original-Sender: categories@mta.ca Precedence: bulk Xref: news.gmane.org gmane.science.mathematics.categories:5822 Archived-At: Perhaps I didn't make it clear that monomorphism is not always the same as 1-1 in a concrete category. As for Peter's suggestion below, the terminology of injective for objects is as well established as the use of the same word for maps. When I was a student, we talked of 1-1 maps and onto maps and I never heard the words injective and surjective. But injective and projective objects followed well-established usage, certainly by the 1950s and probably well before. Somebody (Mac Lane?) once tried using fascist, dual to free, instead of injective. But of course, not every projective is free and, in any case, this never got any traction. Michael On Wed, 19 May 2010, Prof. Peter Johnstone wrote: > Like Michael, I've occasionally been bothered by the conflict between > the two uses of "injective". However, for me it's the use of the word > as a dual for "projective" that feels wrong; the opposite of "pro" is > not "in" but "con" (or "contra"). Also, the use of "injective" > and "surjective" for maps is so well established throughout > mathematics that I don't think there is any chance of changing it. > I've thought of using "coprojective" for the dual of "projective"; > but for anyone with a classical education that word means > "shit-throwing". > > Peter Johnstone [For admin and other information see: http://www.mta.ca/~cat-dist/ ]