From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from lists.gentoo.org (pigeon.gentoo.org [208.92.234.80]) by finch.gentoo.org (Postfix) with ESMTP id 0A3361381F3 for ; Wed, 24 Jul 2013 20:15:32 +0000 (UTC) Received: from pigeon.gentoo.org (localhost [127.0.0.1]) by pigeon.gentoo.org (Postfix) with SMTP id BAD0EE0957; Wed, 24 Jul 2013 20:15:26 +0000 (UTC) Received: from smtp.cs.nyu.edu (SMTP.CS.NYU.EDU [128.122.49.97]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (No client certificate requested) by pigeon.gentoo.org (Postfix) with ESMTPS id B9898E0822 for ; Wed, 24 Jul 2013 20:15:25 +0000 (UTC) Received: from newlap-wireless.localdomain (ool-182de1a5.dyn.optonline.net [24.45.225.165]) (authenticated bits=0) by smtp.cs.nyu.edu (8.14.3/8.14.4) with ESMTP id r6OKFIDw027952 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-SHA bits=256 verify=NOT) for ; Wed, 24 Jul 2013 16:15:22 -0400 (EDT) Received: by newlap-wireless.localdomain (Postfix, from userid 1000) id 47A2DA03D8; Wed, 24 Jul 2013 16:15:18 -0400 (EDT) From: gottlieb@nyu.edu To: gentoo-user@lists.gentoo.org Subject: Re: [gentoo-user] Portage 2.2 References: <20130724111708.447eaa91@hactar.digimed.co.uk> <51EFB0A3.9070309@gmail.com> <20130724200621.GA3609@Gee-Mi-Ni.home> Date: Wed, 24 Jul 2013 16:15:18 -0400 In-Reply-To: <20130724200621.GA3609@Gee-Mi-Ni.home> (Willie WY Wong's message of "Wed, 24 Jul 2013 22:06:21 +0200") Message-ID: <87siz3r9yh.fsf@nyu.edu> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/24.3 (gnu/linux) Precedence: bulk List-Post: List-Help: List-Unsubscribe: List-Subscribe: List-Id: Gentoo Linux mail X-BeenThere: gentoo-user@lists.gentoo.org Reply-to: gentoo-user@lists.gentoo.org MIME-Version: 1.0 Content-Type: text/plain X-Archives-Salt: 26298670-dc1d-49c4-97a2-e37e0464c1f4 X-Archives-Hash: 919372b953ac9f542f512ea0e752d894 On Wed, Jul 24 2013, Willie WY Wong wrote: > Speaking as a mathematician (and A. Gottlieb will agree with me), I > would be rather annoyed that they chose (if this is not a misquote > from the original proposed documentation) to use '/' for set > difference instead of '\' as it is supposed to be. I was also surprised to see `/'. A part of me was going to send about quotient groups (the normal usage of '/') but I managed to refrain myself. However, now that willie has opened the door ... / is normally used for quotients. For example, if we take the group Z of integers under addition and the subgroup 2Z of the even integers, then Z / 2Z is the quotient that results from taking Z and identifying all the elements of 2Z. So in Z / 2Z, all the even integers are zero and hence all odd integers are equivalent (since they differ by even integers, which are zero). Thus the quotient has only 2 elements and is the familiar group Z2, the integers mod 2. The above can be generalized. allan