From mboxrd@z Thu Jan 1 00:00:00 1970 X-Msuck: nntp://news.gmane.io/gmane.science.mathematics.categories/5460 Path: news.gmane.org!not-for-mail From: David Roberts Newsgroups: gmane.science.mathematics.categories Subject: Re: evil (fwd) Re: Quantum computation and categories Date: Sun, 3 Jan 2010 20:31:48 +1030 Message-ID: References: Reply-To: David Roberts NNTP-Posting-Host: lo.gmane.org Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 X-Trace: ger.gmane.org 1262531219 11607 80.91.229.12 (3 Jan 2010 15:06:59 GMT) X-Complaints-To: usenet@ger.gmane.org NNTP-Posting-Date: Sun, 3 Jan 2010 15:06:59 +0000 (UTC) To: categories@mta.ca Original-X-From: categories@mta.ca Sun Jan 03 16:06:52 2010 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 4.50) id 1NRS2d-00013T-Kn for gsmc-categories@m.gmane.org; Sun, 03 Jan 2010 16:06:51 +0100 Original-Received: from Majordom by mailserv.mta.ca with local (Exim 4.61) (envelope-from ) id 1NRRmo-0000OP-QQ for categories-list@mta.ca; Sun, 03 Jan 2010 10:50:30 -0400 In-Reply-To: Original-Sender: categories@mta.ca Precedence: bulk Xref: news.gmane.org gmane.science.mathematics.categories:5460 Archived-At: > but in general, evil exists. every > functor can be factored as an identity-on-the-objects-functor (ioof), > followed by an embedding. the embedding is good, but ioofs are evil, and i > think that they deserve their name. lord knows how much we use them. An ioof is 'evil' in a subtly different way to what was discussed, in my opinion, in that the property of being such a functor is not invariant under natural isomorphism. This is then really a 2-categorical notion of evil. Are there many examples/other commonly used properties of functors that are evil in this way? Happy new year David [For admin and other information see: http://www.mta.ca/~cat-dist/ ]