From mboxrd@z Thu Jan 1 00:00:00 1970 X-Msuck: nntp://news.gmane.io/gmane.science.mathematics.categories/4528 Path: news.gmane.org!not-for-mail From: Bill Lawvere Newsgroups: gmane.science.mathematics.categories Subject: Re: KT Chen's smooth CCC, a correction Date: Wed, 27 Aug 2008 14:23:46 -0400 (EDT) Message-ID: Reply-To: Regula Honegger NNTP-Posting-Host: main.gmane.org Mime-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII; format=flowed X-Trace: ger.gmane.org 1241020006 13715 80.91.229.2 (29 Apr 2009 15:46:46 GMT) X-Complaints-To: usenet@ger.gmane.org NNTP-Posting-Date: Wed, 29 Apr 2009 15:46:46 +0000 (UTC) To: categories@mta.ca Original-X-From: rrosebru@mta.ca Wed Aug 27 16:44:46 2008 -0300 Return-path: Envelope-to: categories-list@mta.ca Delivery-date: Wed, 27 Aug 2008 16:44:46 -0300 Original-Received: from Majordom by mailserv.mta.ca with local (Exim 4.61) (envelope-from ) id 1KYQwX-0002Kj-8H for categories-list@mta.ca; Wed, 27 Aug 2008 16:44:37 -0300 Original-Sender: cat-dist@mta.ca Precedence: bulk X-Keywords: X-UID: 64 Original-Lines: 95 Xref: news.gmane.org gmane.science.mathematics.categories:4528 Archived-At: Dear Ronnie and Colleagues, Your comments are extremely interesting. Thank you very much for raising in so striking a manner the question of the relation between general monoidal structures and cartesian closed structures. Below are some observations which show, I think, that everybody should be interested in this relation because it is manyfold and fruitful. (1) While cartesian closed structures have the virtue of being unique, general monoidal closed structures have the virtue of not being unique. Thus, for example, the cartesian closed presheaf toposes (with their exactness properties and combinatorial truth object) often have a further monoidal closed structure given by Brian Day's convolution with respect to a pro-co-monoidal structure on the site. Cubical as well as simplicial sets have both cartesian and non-cartesian closed structures, and that is 'true', not merely 'convenient'. (2) Another category having both cartesian and non-cartesian monoidal structures is the real interval from zero to infinity with 'x dominates y' as the morphism from x to y. (Actually, this category is derived by collapsing a natural topos of dynamical systems in 'Taking categories seriously' TAC Reprints.) Categories enriched with respect to the non-cartesian structure here (see 'Metric Spaces' TAC reprints) arise every day in analysis and the rich insights of enrichment theory (Functor categories, bi-module composition, free categories, etcetera) should be systematically applied to the advance of analysis and geometry, while on the other hand metric examples inspire further developments of enrichment theory. Cauchy (who never worked on idempotent splitting in ordinary categories and additive categories in the way that Freyd and Karoubi did) does not deserve to have his name brandished as a joke to scare one's uncomprehending colleagues in analysis. The kind of completeness that is inspired by two-sided intervals (unlike the one-sided intervals inaccurately alluded to in common discussions of 'density') indeed reduces to the one attributed to Cauchy in the particular example of Metric Spaces. The author hoped that observation would contribute to the advance of analysis and the development of enrichment theory, not to the supply of buzzwords. In fact, there is an insufficiently known branch of analysis called 'Idempotent Analysis', which deals largely with composition of bi-modules, or more precisely, with the relation between the two closed structures on the infinite interval. Of course, that monoidal category is isomorphic to the unit interval under multiplication (still cartesian closed too) which induces many of the relations between probablility and entropy. (3) Perhaps the most common relation between non-cartesian monoidal categories and cartesian categories arises when a structure such as vector space is interpreted in a cohesive background. I am sticking to my story that cohesive backgrounds are basically cartesian closed, due to the ubiquitous role of diagonal maps and also due to the fact that, for example, bornological vector spaces have an obvious monoidal closed structure, whereas topological vector spaces have none. The rumor that topological vector spaces might have a tensor with an adjoint hom is part of the disinformation that makes functional analysis look more difficult than it is. A more accurate account of the relation between non-Mackey convergence and closed structure can be found in C. Houzel's paper on Grauert finiteness, Mathematische Annalen, vol. 205, 1973, 13-54: essentially, the topological categories are merely enriched in the genuinely monoidal closed bornological ones. Similarly, the idea that not all dual spaces are complete seems to be based on a misguided generality in the notion of Cauchy nets (they should be bounded). (4) Although pointed spaces are somewhat entrenched in algebraic topology, there is an improvement suggested by your own work, Ronnie. Consider the category whose objects are arrows S ---> E where E is a space (object of a cartesian closed cohesive background category) and S is a discrete space. This category is even a topos if the category of E's was, as is the larger category of arrows between general pairs of spaces. The first category is actually an adjoint retract of the second, correcting the discontinuity that arises from the traditional limitation S = 1. Intuitively, in the case where the pair of spaces is a subspace inclusion, the adjoint collapses the subspace to a point if the subspace is connected, but if it is not connected, does not artificially merge its components. There are many applications of this corrected construction of the space which results from 'neglecting' a subspace, both in algebraic topology and in functional analysis, too numerous to discuss here. Bill On Wed, 27 Aug 2008, R Brown wrote: > Dear Bill and Colleagues, > > I would like to explain my own interest in function spaces and function > objects since it has a different origin to what Bill explains and a > different direction which could be of interest for comment and > investigation. ...