From mboxrd@z Thu Jan 1 00:00:00 1970 X-Msuck: nntp://news.gmane.io/gmane.science.mathematics.categories/2902 Path: news.gmane.org!not-for-mail From: Miles Gould Newsgroups: gmane.science.mathematics.categories Subject: Re: Semigroups with many objects Date: Fri, 25 Nov 2005 17:51:45 +0000 Message-ID: <20051125175145.A544@assyrian.org.uk> References: <1e8.47042c41.30b7e030@aol.com> NNTP-Posting-Host: main.gmane.org Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii X-Trace: ger.gmane.org 1241018974 6305 80.91.229.2 (29 Apr 2009 15:29:34 GMT) X-Complaints-To: usenet@ger.gmane.org NNTP-Posting-Date: Wed, 29 Apr 2009 15:29:34 +0000 (UTC) To: categories@mta.ca Original-X-From: rrosebru@mta.ca Fri Nov 25 17:10:33 2005 -0400 Return-path: Envelope-to: categories-list@mta.ca Delivery-date: Fri, 25 Nov 2005 17:10:33 -0400 Original-Received: from Majordom by mailserv.mta.ca with local (Exim 4.52) id 1Efkoi-0005Sj-9A for categories-list@mta.ca; Fri, 25 Nov 2005 17:09:12 -0400 Content-Disposition: inline User-Agent: Mutt/1.2.5i In-Reply-To: <1e8.47042c41.30b7e030@aol.com>; from Topos8@aol.com on Thu, Nov 24, 2005 at 10:34:08PM -0500 Original-Sender: cat-dist@mta.ca Precedence: bulk X-Keywords: X-UID: 47 Original-Lines: 31 Xref: news.gmane.org gmane.science.mathematics.categories:2902 Archived-At: On Thu, Nov 24, 2005 at 10:34:08PM -0500, Topos8@aol.com wrote: > I don't like the term "semigroupoids" because it evokes (for me) the notion > of invertibility which I want to avoid. Google's not a perfect metric for popularity, but it returns about 350 hits for "semigroupoid", about 10 for "fair category", and none for "near category" (the one hit it returns is spurious). Wikipedia has an entry for "semigroupoid" (with the definition you're thinking of) and nothing on any of the others. Looking at MathSciNet, we find 180 hits for "semigroupoid", none for "fair category", and one for "near category". It's worse than that, though, because that paper uses "near category" to mean something different, namely a category-like object with identities but without associativity! All this suggests to me that "semigroupoid" is the standard term, and certainly it's the only one I've ever heard before. I don't think you need to worry about implied invertibility: if you know what both a groupoid and a semigroup are, the term "semigroupoid" strongly suggests a multi-object structure with associatively-composable arrows, but not necessarily with identities. At least, it suggests that to me :-) Hope that helps, Miles -- If you want to see your plays performed the way you wrote them, become President. -- Vaclav Havel