From mboxrd@z Thu Jan 1 00:00:00 1970 X-Msuck: nntp://news.gmane.io/gmane.science.mathematics.categories/6080 Path: news.gmane.org!not-for-mail From: Andrew Stacey Newsgroups: gmane.science.mathematics.categories Subject: Re: Another question on Grothendieck Date: Mon, 30 Aug 2010 20:04:43 +0200 Message-ID: References: Reply-To: Andrew Stacey NNTP-Posting-Host: lo.gmane.org Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii X-Trace: dough.gmane.org 1283299232 6835 80.91.229.12 (1 Sep 2010 00:00:32 GMT) X-Complaints-To: usenet@dough.gmane.org NNTP-Posting-Date: Wed, 1 Sep 2010 00:00:32 +0000 (UTC) Cc: Categories list To: Michael Barr Original-X-From: majordomo@mlist.mta.ca Wed Sep 01 02:00:30 2010 Return-path: Envelope-to: gsmc-categories@m.gmane.org Original-Received: from smtpx.mta.ca ([138.73.1.138]) by lo.gmane.org with esmtp (Exim 4.69) (envelope-from ) id 1OqakZ-00056i-Nm for gsmc-categories@m.gmane.org; Wed, 01 Sep 2010 02:00:23 +0200 Original-Received: from mlist.mta.ca ([138.73.1.63]:44799) by smtpx.mta.ca with esmtp (Exim 4.71) (envelope-from ) id 1Oqaj6-0002yE-0z; Tue, 31 Aug 2010 20:58:52 -0300 Original-Received: from majordomo by mlist.mta.ca with local (Exim 4.71) (envelope-from ) id 1Oqaj2-0004kH-9P for categories-list@mlist.mta.ca; Tue, 31 Aug 2010 20:58:48 -0300 Content-Disposition: inline In-Reply-To: Precedence: bulk Xref: news.gmane.org gmane.science.mathematics.categories:6080 Archived-At: On Mon, Aug 30, 2010 at 10:18:30AM -0400, Michael Barr wrote: > Grothendieck introduces, on the top of p. 209 of the Tohoku paper, the > notation U_{i_0..i_p} without explanation and uses it again over the next > couple pages. Here {U_i} is an open cover of a space X and I have reason > to believe that this stands for the intersection of U_{i_j}. Can anyone > confirm this? Or give an alternate explanation? > > The context is that of a claim that (when A is a sheaf) and "every > U_{i_0..i_p} is A-acyclic, then"... and that awfully like the definition of > a simple cover. I have absolutely no idea as to what Grothendieck meant, but the notation you describe is quite common in (algebraic) topology and means what you "have reason to believe" that it means. Andrew [For admin and other information see: http://www.mta.ca/~cat-dist/ ]