From mboxrd@z Thu Jan 1 00:00:00 1970 X-Msuck: nntp://news.gmane.io/gmane.science.mathematics.categories/2575 Path: news.gmane.org!not-for-mail From: Andree Ehresmann Newsgroups: gmane.science.mathematics.categories Subject: Re: Who invented n-categories? Date: Thu, 26 Feb 2004 19:52:29 +0100 Message-ID: References: <159.2e745aaa.2d6b7dcf@aol.com> NNTP-Posting-Host: main.gmane.org Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii"; format=flowed X-Trace: ger.gmane.org 1241018756 4801 80.91.229.2 (29 Apr 2009 15:25:56 GMT) X-Complaints-To: usenet@ger.gmane.org NNTP-Posting-Date: Wed, 29 Apr 2009 15:25:56 +0000 (UTC) To: cat-dist@mta.ca Original-X-From: rrosebru@mta.ca Fri Feb 27 11:38:19 2004 -0400 Return-path: Envelope-to: categories-list@mta.ca Delivery-date: Fri, 27 Feb 2004 11:38:19 -0400 Original-Received: from Majordom by mailserv.mta.ca with local (Exim 4.10) id 1Awk49-00005M-00 for categories-list@mta.ca; Fri, 27 Feb 2004 11:38:17 -0400 X-Sender: ehres@mailx.u-picardie.fr X-Mailer: QUALCOMM Windows Eudora Version 5.1 In-Reply-To: <159.2e745aaa.2d6b7dcf@aol.com> Original-Sender: cat-dist@mta.ca Precedence: bulk X-Keywords: X-UID: 41 Original-Lines: 27 Xref: news.gmane.org gmane.science.mathematics.categories:2575 Archived-At: In answer to Carl Futia The first given example of a strict 2-category is the example of a 2-category of natural transformations. It has been given by Charles Ehresmann in his paper "Foncteurs types" of 1960 (reprinted in "Charles Ehresmann: Oeuvres completes et commentees" Part IV-1, page 103). He does not give the name 2-category but he explicits the "permutability" of the two laws of which Godement had given some particular cases in his book on sheaf theory in 1958. It is this example as well as the double category of squares of a category (which Charles called 'quatuors' and defined about the same time) that suggested the definition of double categories. I don't know who introduced the name 2-category nor when, but I remembers that Benabou used it around 1962-63. The general definition of an n-fold category is given by Charles in his paper "Categories structurees" in 1963 (reprinted in the "Oeuvres" Part III-1, p. 68), as an example of the general notion of an internal category in a concrete category (which he then called a structured category). The particular case of (strict) n-categories is not specified there. We used it in the last series of papers I wrote with Charles on n-fold categories in 1978 (reprinted in "Oeuvres", Part IV-2, p. 681, but it was well-known by this time. Andree C. Ehresmann