From mboxrd@z Thu Jan 1 00:00:00 1970 X-Msuck: nntp://news.gmane.io/gmane.science.mathematics.categories/1418 Path: news.gmane.org!not-for-mail From: Michael Barr Newsgroups: gmane.science.mathematics.categories Subject: My posting Date: Sat, 12 Feb 2000 19:20:46 -0500 (EST) Message-ID: NNTP-Posting-Host: main.gmane.org Mime-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII X-Trace: ger.gmane.org 1241017818 31166 80.91.229.2 (29 Apr 2009 15:10:18 GMT) X-Complaints-To: usenet@ger.gmane.org NNTP-Posting-Date: Wed, 29 Apr 2009 15:10:18 +0000 (UTC) To: Categories list Original-X-From: rrosebru@mta.ca Sun Feb 13 10:36:08 2000 -0400 Original-Received: (from Majordom@localhost) by mailserv.mta.ca (8.9.3/8.9.3) id JAA09642 for categories-list; Sun, 13 Feb 2000 09:47:44 -0400 (AST) X-Authentication-Warning: triples.math.mcgill.ca: barr owned process doing -bs X-Sender: barr@triples.math.mcgill.ca Original-Sender: cat-dist@mta.ca Precedence: bulk Original-Lines: 9 Xref: news.gmane.org gmane.science.mathematics.categories:1418 Archived-At: >>From Todd Wilson, I learned that adding identities is not so harmless. So suppose only that there are objects, arrows, source and target and arrows that compose associatively only when source matches target. With identities, you can conclude, for any idempotent e, from eee = e1e, that e = 1 and that makes it trivial. Michael