From mboxrd@z Thu Jan 1 00:00:00 1970 X-Msuck: nntp://news.gmane.io/gmane.science.mathematics.categories/10878 Path: news.gmane.io!.POSTED.blaine.gmane.org!not-for-mail From: Vaughan Pratt Newsgroups: gmane.science.mathematics.categories Subject: Re: Non-cartesian closedness of Met (ptj@maths.cam.ac.uk) Date: Fri, 16 Dec 2022 16:27:13 -0800 Message-ID: References: Reply-To: Vaughan Pratt Mime-Version: 1.0 Content-Type: text/plain; charset="UTF-8" Injection-Info: ciao.gmane.io; posting-host="blaine.gmane.org:116.202.254.214"; logging-data="32372"; mail-complaints-to="usenet@ciao.gmane.io" To: Categories mailing list Original-X-From: majordomo@rr.mta.ca Sat Dec 17 23:02:33 2022 Return-path: Envelope-to: gsmc-categories@m.gmane-mx.org Original-Received: from smtp2.mta.ca ([198.164.44.75]) by ciao.gmane.io with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.92) (envelope-from ) id 1p6fGL-0008CV-BE for gsmc-categories@m.gmane-mx.org; Sat, 17 Dec 2022 23:02:33 +0100 Original-Received: from rr.mta.ca ([198.164.44.159]:37386) by smtp2.mta.ca with esmtp (Exim 4.80) (envelope-from ) id 1p6fFt-0003tS-CH; Sat, 17 Dec 2022 18:02:05 -0400 Original-Received: from majordomo by rr.mta.ca with local (Exim 4.92.1) (envelope-from ) id 1p6fF4-0000j4-Md for categories-list@rr.mta.ca; Sat, 17 Dec 2022 18:01:14 -0400 Precedence: bulk Xref: news.gmane.io gmane.science.mathematics.categories:10878 Archived-At: Peter, can you generalize your argument to a necessary and sufficient condition on V such that the usual closed structure on V-Cat is cartesian? This is of interest for its applicability to models of concurrent computation, as follows. My group's 1989 paper "Temporal Structures", http://boole.stanford.edu/pub/man90.pdf presented at CTCS-89 in Manchester and later in journal form as Mathematical Structures in Computer Science, Volume 1:2, 179-213 (July 1991), had the following abstract. "We combine the principles of the Floyd-Warshall-Kleene algorithm, enriched categories, and Birkhoff arithmetic, to yield a useful class of algebras of transitive vertex-labeled spaces. The motivating application is a uniform theory of abstract or parametrized time in which to any given notion of time there corresponds an algebra of concurrent behaviors and their operations, always the same operations but interpreted automatically and appropriately for that notion of time. An interesting side application is a language for succinctly naming a wide range of datatypes." A little later I noticed that the structures treated there were starting to look like those in Girard's recent (1986) work on linear logic, and wrote about that as Section 5 in my CONCUR-92 paper "The Duality of Time and Information", http://boole.stanford.edu/pub/dti.pdf. (I like to think of Ecclesiastes 9:11, "but time and chance happeneth to them all" as an early appearance of that duality via Shannon's statistical view of information, and the bras and kets of quantum mechanics as a later one.) The idea of orthocurrence (the monoid in a closed monoidal category) as interaction, and its adjoining closed structure as observation, is spelled out more explicitly in a talk I gave at an IJCAI'01 workshop on spatial and temporal reasoning in Seattle in 2001 organized by NSF's Frank Anger. Slides (cryptic): http://boole.stanford.edu/pub/ijcaitalk.pdf Paper (detailed): http://boole.stanford.edu/pub/ortho.pdf, unpublished but later incorporated into Paper (far more detailed): http://boole.stanford.edu/pub/seqconc.pdf What got me into all this in the beginning was noticing in the mid-1980s that in the obvious generalization of ordered time (Pos) to real time (Met), the closed monoidal structure ceased to be cartesian and the single operation of orthocurrence now split into two monoids, one closed and the other cartesian. That's when I noticed the similarity to Girard's linear logic, which had made the same split independently and at the same time but for a totally different application, substructural logic. The connection was completed once I'd figured out the duality of time and information as in Ezekiel 9:11. For Vineet Gupta's thesis in 1991 I suggested choosing between that duality and cubical complexes as a geometric model of concurrency. After looking at both for a month Vineet picked the former. At POPL'91 Boris Trakhtenbrot asked me at question time how the two could be connected, which I was unable to do until realizing (too late for Vineet who'd finished his thesis by then) that Chu(Set,3) provided the edges, faces, etc. of the cubical complexes by interpreting 3 as {0, 1/2, 1} with each face's dimension given by the number of 1/2's (transitions) appearing in it. Vaughan Pratt [For admin and other information see: http://www.mta.ca/~cat-dist/ ]