From mboxrd@z Thu Jan 1 00:00:00 1970 X-Msuck: nntp://news.gmane.io/gmane.science.mathematics.categories/1744 Path: news.gmane.org!not-for-mail From: Jean Benabou Newsgroups: gmane.science.mathematics.categories Subject: Terminology Date: Tue, 12 Dec 2000 08:19:37 +0000 Message-ID: <19914.5274273635$1241018064@news.gmane.org> NNTP-Posting-Host: main.gmane.org Mime-Version: 1.0 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: 8bit X-Trace: ger.gmane.org 1241018063 32707 80.91.229.2 (29 Apr 2009 15:14:23 GMT) X-Complaints-To: usenet@ger.gmane.org NNTP-Posting-Date: Wed, 29 Apr 2009 15:14:23 +0000 (UTC) To: Category list Original-X-From: rrosebru@mta.ca Tue Dec 12 17:03:39 2000 -0400 Return-Path: Original-Received: (from Majordom@localhost) by mailserv.mta.ca (8.11.1/8.11.1) id eBCKBgr06947 for categories-list; Tue, 12 Dec 2000 16:11:42 -0400 (AST) X-Authentication-Warning: mailserv.mta.ca: Majordom set sender to cat-dist@mta.ca using -f X-Mailer: Microsoft Internet Mail & News for Macintosh - 3.0 X-MIME-Autoconverted: from quoted-printable to 8bit by mailserv.mta.ca id eBC73rt15252 Original-Sender: cat-dist@mta.ca Precedence: bulk X-Keywords: X-UID: 17 Original-Lines: 26 Xref: news.gmane.org gmane.science.mathematics.categories:1744 Archived-At: I am confronted with problems of "contradictory terminology" which I would like to solve and, since english is not my language, I need some suggestions. Let F: Y-----> X be a functor such that for every object x of X the comma category (x,F) is connected.Such functors, although they are not defined in all generality, are called "cofinal" in SGA 4 , and "initial" in Borceux's handbook (Vol.1-§2.11-p.69) but none of these terms is satisfactory. The "cofinal" name comes obviously from the vocabulary of ordered sets which are special cases, but in category theory "co" is now associated with dual notions. The "initial" name is even less satisfactory, because: (i) If Y=1, F is identified with an object x of X and F is "initial" iff x is a terminal object of X ! (ii) More generally, if Y has a terminal object t then F is "initial" iff F(t) is terminal ! (iii) Even more generally yet, without assuming the existence of terminal objects in Y or X : Let X^ and Y^ be the categories of presheaves on X and Y, and F! :X^-----> Y^ the canonical extension of F to these categories.If T is the terminal object of Y^ one can easily show that F has the previous property iff F!(T) is terminal in X^.(Which by the way, gives the nicest proof of the stability under composition of such functors) I propose to call these functors either "terminal" or better "final" but I would like to know if this would not conflict with previous terminology. Thanks for your help.