From mboxrd@z Thu Jan 1 00:00:00 1970 X-Msuck: nntp://news.gmane.io/gmane.science.mathematics.categories/3585 Path: news.gmane.org!not-for-mail From: "David Espinosa" Newsgroups: gmane.science.mathematics.categories Subject: Re: Grothendieck construction Date: Fri, 19 Jan 2007 10:44:48 -0800 Message-ID: NNTP-Posting-Host: main.gmane.org Mime-Version: 1.0 Content-Type: text/plain;format=flowed;charset="iso-8859-1";reply-type=original Content-Transfer-Encoding: 7bit X-Trace: ger.gmane.org 1241019392 9356 80.91.229.2 (29 Apr 2009 15:36:32 GMT) X-Complaints-To: usenet@ger.gmane.org NNTP-Posting-Date: Wed, 29 Apr 2009 15:36:32 +0000 (UTC) To: Original-X-From: rrosebru@mta.ca Fri Jan 19 19:42:59 2007 -0400 Return-path: Envelope-to: categories-list@mta.ca Delivery-date: Fri, 19 Jan 2007 19:42:59 -0400 Original-Received: from Majordom by mailserv.mta.ca with local (Exim 4.61) (envelope-from ) id 1H83Hw-0002I0-3S for categories-list@mta.ca; Fri, 19 Jan 2007 19:36:52 -0400 Original-Sender: cat-dist@mta.ca Precedence: bulk X-Keywords: X-UID: 78 Original-Lines: 23 Xref: news.gmane.org gmane.science.mathematics.categories:3585 Archived-At: > "he knew it long before Grothendieck..." So maybe the construction itself is obvious, particularly if you know the semi-direct product or some other specialization (of the general construction). But the intrinic characterization of what the construction yields, that is, the definition of a fibration, seems less obvious. I'm sure everyone has a favorite example of that. For example, Carsten Fuhrmann gave an intrinsic description of the Kleisli category of a monad only in 1999. His home page is: http://www.cs.bath.ac.uk/~cf/ David