From mboxrd@z Thu Jan 1 00:00:00 1970 X-Msuck: nntp://news.gmane.io/gmane.science.mathematics.categories/2944 Path: news.gmane.org!not-for-mail From: "Clemens.BERGER" Newsgroups: gmane.science.mathematics.categories Subject: Re: name for a concept Date: Thu, 08 Dec 2005 12:26:08 +0100 Organization: Laboratoire J.-A. =?ISO-8859-1?Q?Dieudonn=E9?= Message-ID: <43981850.2080902@math.unice.fr> Reply-To: cberger@math.unice.fr NNTP-Posting-Host: main.gmane.org Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit X-Trace: ger.gmane.org 1241018998 6451 80.91.229.2 (29 Apr 2009 15:29:58 GMT) X-Complaints-To: usenet@ger.gmane.org NNTP-Posting-Date: Wed, 29 Apr 2009 15:29:58 +0000 (UTC) To: categories@mta.ca Original-X-From: rrosebru@mta.ca Fri Dec 9 09:34:45 2005 -0400 Return-path: Envelope-to: categories-list@mta.ca Delivery-date: Fri, 09 Dec 2005 09:34:45 -0400 Original-Received: from Majordom by mailserv.mta.ca with local (Exim 4.52) id 1EkiJ7-0004JL-Ii for categories-list@mta.ca; Fri, 09 Dec 2005 09:29:05 -0400 User-Agent: Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.6) Gecko/20040116 X-Accept-Language: en-us, en Original-Sender: cat-dist@mta.ca Precedence: bulk X-Keywords: X-UID: 19 Original-Lines: 13 Xref: news.gmane.org gmane.science.mathematics.categories:2944 Archived-At: In my previous message, one should read: a commutative square with two parallel fibrations in a right proper model category is a homotopy pullback if and only if the square is exact with respect to the class of weak equivalences. These special squares compose because weak equivalences are stable under base change along fibrations (this is the definition of right proper). Clemens Berger.