From mboxrd@z Thu Jan 1 00:00:00 1970 X-Msuck: nntp://news.gmane.io/gmane.science.mathematics.categories/6559 Path: news.gmane.org!not-for-mail From: "Vasili I. Galchin" Newsgroups: gmane.science.mathematics.categories Subject: sieves in nLab Date: Tue, 1 Mar 2011 13:18:44 -0600 Message-ID: Reply-To: "Vasili I. Galchin" NNTP-Posting-Host: lo.gmane.org Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 X-Trace: dough.gmane.org 1299027337 5645 80.91.229.12 (2 Mar 2011 00:55:37 GMT) X-Complaints-To: usenet@dough.gmane.org NNTP-Posting-Date: Wed, 2 Mar 2011 00:55:37 +0000 (UTC) To: Categories mailing list Original-X-From: majordomo@mlist.mta.ca Wed Mar 02 01:55:30 2011 Return-path: Envelope-to: gsmc-categories@m.gmane.org Original-Received: from smtpx.mta.ca ([138.73.1.114]) by lo.gmane.org with esmtp (Exim 4.69) (envelope-from ) id 1PuaLi-00013j-LP for gsmc-categories@m.gmane.org; Wed, 02 Mar 2011 01:55:30 +0100 Original-Received: from mlist.mta.ca ([138.73.1.63]:38291) by smtpx.mta.ca with esmtp (Exim 4.71) (envelope-from ) id 1PuaLc-0002HM-5Y; Tue, 01 Mar 2011 20:55:24 -0400 Original-Received: from majordomo by mlist.mta.ca with local (Exim 4.71) (envelope-from ) id 1PuaLX-0005RF-S5 for categories-list@mlist.mta.ca; Tue, 01 Mar 2011 20:55:20 -0400 Precedence: bulk Xref: news.gmane.org gmane.science.mathematics.categories:6559 Archived-At: Hello, I am confused about the notion of "encoding" regarding sieves: ." And sieves on objects are mostly used in the context of Grothendieck topologies to encode presheaves that behave like coverings" "Sieves are an equivalent way to encode subobjects of representable functors in a presheaf category in terms of the total sets of elements of such a subfunctor." "It is in this way that sieves and their associated subfunctors encode the notion of cover of an object V: they tell us which of all the maps into V do factor through the cover." Regards, Vasili [For admin and other information see: http://www.mta.ca/~cat-dist/ ]