From mboxrd@z Thu Jan 1 00:00:00 1970 X-Msuck: nntp://news.gmane.io/gmane.science.mathematics.categories/4491 Path: news.gmane.org!not-for-mail From: John Baez Newsgroups: gmane.science.mathematics.categories Subject: spans in 2-categories Date: Tue, 19 Aug 2008 07:45:12 -0700 Message-ID: NNTP-Posting-Host: main.gmane.org Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii X-Trace: ger.gmane.org 1241019979 13555 80.91.229.2 (29 Apr 2009 15:46:19 GMT) X-Complaints-To: usenet@ger.gmane.org NNTP-Posting-Date: Wed, 29 Apr 2009 15:46:19 +0000 (UTC) To: categories Original-X-From: rrosebru@mta.ca Tue Aug 19 13:59:01 2008 -0300 Return-path: Envelope-to: categories-list@mta.ca Delivery-date: Tue, 19 Aug 2008 13:59:01 -0300 Original-Received: from Majordom by mailserv.mta.ca with local (Exim 4.61) (envelope-from ) id 1KVUXk-0005Wd-OJ for categories-list@mta.ca; Tue, 19 Aug 2008 13:58:52 -0300 Content-Disposition: inline Original-Sender: cat-dist@mta.ca Precedence: bulk X-Keywords: X-UID: 26 Original-Lines: 20 Xref: news.gmane.org gmane.science.mathematics.categories:4491 Archived-At: Dear Categorists - Given a category C with pullbacks we can define a bicategory Span(C) where objects are objects of C, morphisms are spans - composed using pullback - and 2-morphisms are maps between spans. Have people tried to categorify this yet? Suppose we have a 2-category C with pseudo-pullbacks. Then we should be able to define a tricategory Span(C). Has someone done this? Or maybe people have gotten some partial results, e.g. in the case where C = Cat. I'd like to know about these! Best, jb