November 1994 - Categories - categories.org.au

history question: Grothendieck universes
by Juergen Koslowski 03 Dec '94

03 Dec '94

Could someone please tell me where the term "Grothendieck universes" comes from? Some books connect Grothendieck's name with this particular approach to avoid set-theoretical difficulties, others don't. What is the current status on these foundational matters anyway? Has anything else emerged besides MacLanes one universe approach, or Feferman's use of reflection principles? best regards, J"urgen -- J"urgen Koslowski | If I don't see you no more in this world | I meet you in the next world koslowj(a)math.ksu.edu | and don't be late! nhabkosl(a)rrzn-user.uni-hannover.de | Jimi Hendrix (Voodoo Child)

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57th PSSL
by damphous＠univ-tours.fr 28 Nov '94

28 Nov '94

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% %%%% TEX SOURCE OF THE ANNOUNCEMENT BELOW %%%% %%%% TEX SOURCE OF THE ANNOUNCEMENT BELOW %%%% %%%% PLAIN TEX PLAIN TEX PLAIN TEX %%%% %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% %&tex %A4 \font\BF=cmbx12 scaled\magstep3 \font\RM=cmr12 \font\SC=cmcsc10 scaled\magstep1 \font\SL=cmsl12 \font\TT=cmtt12 \baselineskip=16pt \narrower %%%%%%%%%%%% \RM $$\hbox{\BF 57th PERIPATETIC SEMINAR}$$ $$\hbox{\BF ON SHEAVES AND LOGIC}$$ \vskip1.6cm \setbox25=\hbox{Dear Colleagues,}\dimen25=\wd25 \noindent\box25\par\medbreak \noindent\kern\dimen25% This is the announcement of % $$\hbox{\SC THE 57th PERIPATETIC SEMINAR ON SHEAVES AND LOGIC}$$ % This PSSL is to be held in Tours on the 18-19th of february. As usual, talks on topics in logic, category theory and related areas in mathematics and computer science are welcome. Please publicize this meeting amongst your colleagues. At the time of the meeting, {\SC Jiri Rosicky\/} will be a guest at the university {\SL Fran\c cois Rabelais\/}. The meeting will be supported by the university for a fixed amount (not known yet), so that what the fees are to be is not even known by the organizer. At this time of the academic year, housing in the halls of residence is impossible. However, the {\SL Centre R\'egional des Oeuvres Universitaires\/}, has now a splendid {\SL petit h\^otel particulier\/}, (this is the modest local name for private small ch\^ateaux that rich families owned along the Loire river) where we will have the 57th PSSL. It has 33 bedrooms, lecture rooms, a nice and huge garden for mathematical meditation\dots\ Meals will be served on the site. The cost is 210FF per night with breakfast, plus 85FF per meal. The place is rated ***; the cost is however inferior to a plain **-hotel. The fees will be equal to $$\hbox{(total cost - money from the university)/(the number of participants)}.$$ If there is a need for more than 33 bedrooms, arrangements will be made for a hotel. So registering as early as possible (if you intend to come) is going to make the organisation easier. As usual, participants will arrive on friday night or on saturday morning. Lectures will start (probably) at 9.30 on staurday and will finish on sunday morning at noon. It will be possible to have diner there on friday and lunch on sunday. I will send all registered mathematicians complete details on the location of {\SL La croix montoire\/}, the name of this ``petit h\^otel particulier''. It is in Tours on the north shore of the Loire river, and can be reached by urban busses from the train station. \vfill\eject $$\hbox{\SC Please return as soon as possible}$$ $$\hbox{e-mail: {\TT damphous(a)univ-tours.fr\/}}$$ $$\hbox{$\matrix{\hbox{\SL Pierre Damphousse}\hfill\cr \hbox{\SL D\'epartement de Math\'ematiques}\hfill\cr \hbox{\SL Facult\'e des Sciences}\hfill\cr \hbox{\SL Parc de Grandmont}\hfill\cr \hbox{\SL Tours 37200, FRANCE}\hfill\cr}$}$$ \vskip1.5cm \noindent I would like to attend the 57th PSSL:\par\smallbreak Name:\par\smallbreak Return Address:\par\smallbreak \vskip3cm email:\par \bigbreak \noindent I wish to give a talk entitled:\par\smallbreak of 20/30/45 minutes (specify):\par \bigbreak \noindent I wish to book accomodation from ..................... to ................;\par\smallbreak I will have diner on friday night (not included in the fees) (Yes/No):\par\smallbreak I will have lunch on sunday (not included in the fees) (Yes/No):\par\smallbreak % \bye

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pssl in Aarhus, second announcement
by unknown＠categories.mta.ca 24 Nov '94

24 Nov '94

---------- Forwarded message ----------

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TLCA '95 : Programme
by unknown＠categories.mta.ca 24 Nov '94

24 Nov '94

\documentstyle{article} \begin{document} \newcommand{\Paper}[2] {{\it #1},$\;${#2}} \title{Programme\\ International Conference on \\ Typed Lambda Calculi and Applications\\ {\normalsize Edinburgh, April 10th - 12th, 1995}} \author{}\date{} \maketitle \begin{tabbing} {\bf MONDAY}\\ Morning Session Chaired by: M.~Dezani\\ {\bf Theory of Reduction and Conversion}\\ 9.00 \Paper{Typed $\lambda$-calculi with explicit substitutions may not terminate} {P.A.~Mellies}\\ 9.30 \Paper{Comparing $\lambda$-calculus translations in sharing graphs} {A.~Asperti, C.~Laneve}\\ 10.00 Coffee\\ 10.30 \Paper{Typed operational semantics}{H.~Goguen}\\ 11.00 \Paper{An explicit eta rewrite rule} {D. Briaud}\\ 11.30 \Paper{$\beta\eta$-equality for coproducts} {N.~Ghani} \\ \\ 12.00 Lunch \\ \\ Afternoon Session Chaired by: G.~Plotkin\\ {\bf Semantics I}\\ 2.00 \= {\it A fully abstract translation between a $\lambda$-calculus with reference types and }\\ \> {\it standard ML,} {E.~Ritter, A.M.~Pitts}\\ 2.30 \Paper{Final semantics for untyped $\lambda$-calculus} {F.~Honsell, M.~Lenisa} \\ 3.00 Tea \\ {\bf Categorical Semantics}\\ 3.30 \Paper{What is a categorical model of intuitionistic linear logic?} {G.M.~Bierman} \\ 4.00 \= {\it Categorical semantics of the call-by-value $\lambda$-calculus,}\\ \> {A.~Pravato, S.~Ronchi della Rocca, L.~Roversi}\\ 4.30 \Paper{Categorical completeness results for the simply-typed $\lambda$-calculus} {A.K.~Simpson} \\ \end{tabbing} \newpage \begin{tabbing} \\ {\bf TUESDAY}\\ Morning Session Chaired by: H.~Barendregt\\ {\bf Type Theory I}\\ 9.00 \Paper{Untyped $\lambda$-calculus with relative typing} {M.R.~Holmes}\\ 9.30 \Paper{Basic properties of data types with inequational refinements} {H.~Kondoh} \\ 10.00 Coffee\\ 10.30 \Paper{Extensions of pure type systems} {G.~Barthe}\\ 11.00 \Paper{A simple calculus of exception handling} {P.~de Groote}\\ {\bf Proof Theory}\\ 11.30 \Paper{Strict functionals for termination proofs} {J.~van de Pol, H.~Schwichtenberg} \\ \\ 12.00 Lunch\\ \\ Afternoon Session Chaired by: F.~Honsell\\ {\bf Semantics II}\\ 2.00 \Paper{A simplification of Girard's paradox} {A.J.~Hurkens}\\ 2.30 \= {\it A realization of the negative interpretation of the Axiom of Choice},\\ \> {S.~Berardi, M.~Bezem, T.~Coquand}\\ 3.00 Tea\\ 3.30 \= {\it A model for formal parametric polymorphism: a per interpretation of}\\ \> {\it system $\cal R$}, {R.~Bellucci, M.~Abadi, P.L.~Curien}\\ 4.00 \Paper{Expanding extensional polymorphism} {R.~Di Cosmo, A.~Piperno}\\ {\bf Discussion}\\ 4.30 Open Problem Session, H. Barendregt\\ \end{tabbing} \begin{tabbing} \\ {\bf WEDNESDAY}\\ Morning Session Chaired by: J.~Smith\\ {\bf Machine Assisted Reasoning I}\\ 9.00 \Paper{A verified typechecker} {R.~Pollack}\\ 9.30 \Paper{Higher-order abstract syntax in Coq} {J.~Despeyroux, A.~Felty, A.~Hirschowitz}\\ 10.00 Coffee\\ {\bf Type Theory II}\\ 10.30 \Paper{Using subtyping in program optimization} {S.~Berardi, L.~Boerio}\\ 11.00 \Paper{A simple model for quotient types} {M.~Hofmann}\\ 11.30 \Paper{$\lambda$-calculus, combinators and comprehension systems} {G.~Dowek}\\ \\ 12.00 Lunch\\ \\ \end{tabbing}\newpage \begin{tabbing} Afternoon Session Chaired by: R.~Hindley\\ {\bf Machine Assisted Reasoning II}\\ 2.00 \Paper{Extracting text from proof} {Y.~Coscoy, G.~Kahn, L.~Thery}\\ 2.30 \= {\it Termination proof of term rewriting system with the multiset path ordering and}\\ \> {\it derivation length. A complete development in the Calculus of Constructions},\\ \> {F.~Leclerc}\\ 3.00 Tea\\ {\bf Decision Problems}\\ 3.30 \Paper{Third-order matching in the presence of type constructors} {J.~Springintveld}\\ 4.00 \Paper{On equivalence classes of interpolation equations} {V.~Padovani}\\ 4.30 \Paper{Decidable properties of intersection type systems} {T.~Kurata, M.~Takahashi}\\ \end{tabbing} \end{document}

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11th ADT Workshop and 8th General Compass Meeting (ASCII & Latex)
by Magne.Haveraaen＠ii.uib.no 23 Nov '94

23 Nov '94

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%ASCII%%%%%%%%%%%%%%%%%%%%%%%%% 11th ADT Workshop and 8th General Compass Meeting September 19 1995 -- September 23 1995 Call for Participation Workshop on Specification of Abstract Data Types and ESPRIT Compass Meeting --------------------------------------------------------------------------- The two joint events will take place at Holmenkollen in Oslo. The workshop starts just after lunch-time Tuesday September 19, and lasts till Saturday evening September 23. Before the workshop a meeting of the IFIP WG 14.3 (Foundations of Systems Specifications) will be held at the same place starting just after lunch-time Monday September 18. The workshop will provide an opportunity to meet colleagues, to present recent and ongoing work and to discuss new ideas and future trends. The workshop is organized by Olaf Owe and Ole-Johan Dahl from the University of Oslo, and Magne Haveraaen from the University of Bergen. The topics of the workshop include, but are not limited to: - algebraic specifications; - other approaches to formal specification; - specification languages and methods; - term rewriting and proof systems; - specification development systems (concepts, tools, etc.). It is planned to have a small number of invited talks. The proceedings, consisting of a selection of the presented talks through the usual referee process, will be published after the workshop, probably in the Lecture Notes series of the Springer-Verlag (see e.g. the Recent Trends in Data Type Specifications series, n. 332, 534, 655, 785, ...). Please note: as there is a limited number of slots for talks, REGISTER NOW! We will accept speakers essentially in the order of arrival date of their registrations (a corrective mechanism is organized in order to guarantee visibility to every site). So if you plan to have a talk please let us know as soon as possible (communication via e-mail or WWW is suggested). Location -------- The workshop will be held at the Soria Moria hotel at Holmenkollen in Oslo. Even though the site is barely 12 km from downtown and 14 km from the airport, the area has a hilly flavour, surrounded by quiet woods, an excellent terrain for walking. The hotel itself is modern with excellent conference facilities, including swimming pool and sauna. Accommodation ------------- According to the tradition, the workshop is planned on a residential base, so participants are required to stay at the Soria Moria hotel. Normal arrival is expected Tuesday September 19 after lunch, and departure on Sunday September 24 after breakfast, with the possibility of extending the stay in both directions. Participants to the IFIP WG 14.3 meeting are expected to arrive Monday September 18 after lunch. We have reserved a number of rooms, both single and double, and expect to be able to accommodate everybody registering BEFORE JUNE 15. We will try to accommodate people registering by July 31, depending on room availability. Deadline for registration is the 15th of June '95 Please note: the single rooms will be assigned essentially following a FIFO principle; thus if you want a single room, book it now. Prices We have an agreement with the hotel for a special price for full board during the workshop. For a single room this amounts to 880 NOK per day, and to 620 NOK per day per person in a double room. For the whole workshop the prices in Norwegian Crowns amount to: ! WADT/COMPASS (Tue-Sun) ! WG14.3/WADT/COMPASS (Mon-Sun) -----------------+-------------------------+------------------------------ single room ! 4400 NOK (ca. 530 ECU) ! 5280 NOK (ca. 640 EQU) double room, p.p.! 3100 NOK (ca. 375 EQU) ! 3720 NOK (ca. 450 ECU) -----------------+-------------------------+------------------------------ Note that the prices in ECU are obtained at the current rate (which could be different next September). There is a small chance that the boarding prices may be influenced by changes in the Norwegian taxation system. Such changes, if any, will be decided before Christmas. Registration fee ---------------- As usual a reasonable fee will be required at the registration desk, to cover expenses like proceedings publication, social events and so on. The precise amount has still to be established, depending on the real costs and the funds that can be raised to cover them. Travel Information ------------------ The Soria Moria hotel is easily reachable by bus and taxi from downtown Oslo or directly from the Fornebu Airport in Oslo. The dates for the event have been chosen so that participants can make use of reduced airfares (PEX, APEX). Other information ----------------- More organizational details will follow, and registered participants will be kept informed. Updated information will also be available on the World-Wide Web (WWW) at URL: http://www.ifi.uio.no/~adt95/ AS THERE IS A LIMITED NUMBER OF PLACES AVAILABLE FOR THE WORKSHOP, REGISTER EARLY! We will accept participants in the order of date of arrival of the enclosed registration form Please return the registration form (by e-mail or surface mail) to the following address. ADT'95 Organization Institutt for informatikk e-mail: adt95(a)ifi.uio.no Postboks 1080 Blindern phone: +47 22 85 24 10 0316 OSLO fax: +47 22 85 24 01 Norway WWW: http://www.ifi.uio.no/~adt95/ ------------------------------------------------------------------------ 11th ADT Workshop and 8th General Compass Meeting Registration form One form for each participant, please! Family Name ........................................................ Christian Name ........................................................ Institution ........................................................ Mailing address ........................................................ ........................................................ ........................................................ ........................................................ ........................................................ E-mail ........................................................ Fax ........................................................ Telephone ........................................................ I will attend to the workshop ... yes ... no I intend to give a talk ... yes ... no If yes, provisional title .............................................. ........................................................ ........................................................ I prefer ... single room ... double room I would like to share the room with ................................ Special meal requirements (please specify): ............................ I will arrive .......................... I will depart .......................... I am a member of IFIP WG 14.3 ... yes ... no Name of accompanying non-participants .................................. for which I need ...... additional single rooms and ...... additional double rooms Signature ............................................................. %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%LATEX%%%%%%%%%%%%%%%%%%%%%%%%% \documentstyle{article} \topmargin - 21mm \oddsidemargin -11mm \evensidemargin -11mm \textheight 256mm \textwidth 180mm \renewcommand{\arraystretch}{1.5} \catcode`\<=\active\global\chardef~126 %\newcommand{\printtilde}{\verb+~+} \pagestyle{empty} \title{{\LARGE\bf 11th ADT Workshop and 8th General Compass Meeting}} \author{{\Large\bf September 19 1995 -- September 23 1995}} \date{{\large\bf Call for Participation}} \begin{document} \maketitle \thispagestyle{empty} \subsection*{Workshop on specification of Abstract Data Types and ESPRIT Compass Meeting} The two joint events will take place at Holmenkollen in Oslo. The workshop starts just after lunch-time Tuesday September 19, and lasts till Saturday evening September 23. Before the workshop a meeting of the IFIP WG 14.3 (Foundations of Systems Specifications) will be held at the same place starting just after lunch-time Monday September 18. \\ The workshop will provide an opportunity to meet colleagues, to present recent and ongoing work and to discuss new ideas and future trends. The workshop is organized by Olaf Owe and Ole-Johan Dahl from the University of Oslo, and Magne Haveraaen from the University of Bergen. The topics of the workshop include, but are not limited to: \begin{itemize} \item algebraic specifications; \item other approaches to formal specification; \item specification languages and methods; \item term rewriting and proof systems; \item specification development systems (concepts, tools, etc.). \end{itemize} It is planned to have a small number of invited talks. The proceedings, consisting of a selection of the presented talks through the usual referee process, will be published after the workshop, probably in the Lecture Notes series of the Springer-Verlag (see e.g.\ the Recent Trends in Data Type Specifications series, n. 332, 534, 655, 785, \ldots). \medskip \noindent{\bf Please note:} as there is a limited number of slots for talks, {\large\em register now!} We will accept speakers essentially in the order of arrival date of their registrations (a corrective mechanism is organized in order to guarantee visibility to every site). So if you plan to have a talk please let us know as soon as possible (communication via e-mail or WWW is suggested). \subsection*{Location} The workshop will be held at the Soria Moria hotel at Holmenkollen in Oslo. Even though the site is barely 12 km from downtown and 14 km from the airport, the area has a hilly flavour, surrounded by quiet woods, an excellent terrain for walking. The hotel itself is modern with excellent conference facilities, including swimming pool and sauna. \subsection*{Accommodation} According to the tradition, the workshop is planned on a residential base, so participants are required to stay at the Soria Moria hotel. Normal arrival is expected Tuesday September 19 after lunch, and departure on Sunday September 24 after breakfast, with the possibility of extending the stay in both directions. Participants to the IFIP WG 14.3 meeting are expected to arrive Monday September 18 after lunch. We have reserved a number of rooms, both single and double, and expect to be able to accommodate everybody registering {\bf before June 15}. We will try to accommodate people registering by July 31, depending on room availability. \begin{center} \large\bf \fbox{Deadline for registration is the 15th of June '95} \end{center} \medskip \noindent{\bf Please note:} the single rooms will be assigned essentially following a {\tt FIFO} principle; thus if you want a single room, {\em book it now}. \subsubsection*{Prices} We have an agreement with the hotel for a special price for full board during the workshop. For a single room this amounts to 880 NOK per day, and to 620 NOK per day per person in a double room. \noindent For the whole workshop the prices in Norwegian Crowns amount to: \smallskip \begin{center} \begin{tabular}{|l|c|c|}\hline & Just WADT/COMPASS (Tue-Sun) & IFIP WG 14.3 \& WADT/COMPASS (Mon-Sun) \\ \hline single room & 4400 NOK ($\approx$ 530 ECU) & 5280 NOK ($\approx$ 640 EQU) \\ \hline double room, p.p. & 3100 NOK ($\approx$ 375 EQU) & 3720 NOK ($\approx$ 450 ECU) \\ \hline \end{tabular} \end{center} \smallskip Note that the prices in ECU are obtained at the current rate (which could be different next September). There is a small chance that the boarding prices may be influenced by changes in the Norwegian taxation system. Such changes, if any, will be decided before Christmas. \medskip \subsection*{Registration fee} As usual a reasonable fee will be required at the registration desk, to cover expenses like proceedings publication, social events and so on. The precise amount has still to be established, depending on the real costs and the funds that can be raised to cover them. \subsection*{Travel Information} The Soria Moria hotel is easily reachable by bus and taxi from downtown Oslo or directly from the Fornebu Airport in Oslo. The dates for the event have been chosen so that participants can make use of reduced airfares (PEX, APEX). \subsection*{Other information} More organizational details will follow, and registered participants will be kept informed. Updated information will also be available on the World-Wide Web (WWW) at URL: \begin{center} http://www.ifi.uio.no/~adt95/ \end{center} \vspace{0.8cm} \noindent{\Large As there is a limited number of places available for the workshop, register early! \ \ \ \ \ \ \noindent We will accept participants in the order of date of arrival of the enclosed registration form \bigskip \begin{center} REGISTER NOW! \end{center} } \vspace{0.8cm} \noindent Please return the registration form (by e-mail or surface mail) to the following address. \begin{center} \begin{tabular}{lcll} ADT'95 Organization &\makebox[3cm]{}& \\ Institutt for informatikk &&e-mail: &adt95(a)ifi.uio.no \\ Postboks 1080 Blindern &&phone: &+47 22 85 24 10 \\ 0316 OSLO &&fax: &+47 22 85 24 01 \\ Norway &&WWW: &http://www.ifi.uio.no/~adt95/ \end{tabular} \end{center} \begin{center} \pagebreak {\Large\bf 11th ADT Workshop and 8th General Compass Meeting} \smallskip {\Large\bf Registration form} {\bf One form for each participant, please!} \end{center} \addtolength{\baselineskip}{0.3cm} \bigskip \noindent \makebox[3cm][l]{Family Name} \ \dotfill\ \\ \makebox[3cm][l]{Christian Name} \ \dotfill\ \\ \makebox[3cm][l]{Institution} \ \dotfill\ \\ \makebox[3cm][l]{Mailing address} \ \dotfill\ \\ \makebox[3cm]{} \ \dotfill\ \\ \makebox[3cm]{} \ \dotfill\ \\ \makebox[3cm]{} \ \dotfill\ \\ E-mail \dotfill\qquad Fax \dotfill\qquad Telephone \dotfill\\ \bigskip \noindent \begin{tabular}{lll} I will attend to the workshop & $\Box$ yes & $\Box$ no\\ I intend to give a talk & $\Box$ yes & $\Box$ no\\ \end{tabular} \hspace{1cm}If yes, provisional title \dotfill\\ \makebox[3cm]{}\dotfill\\ \bigskip \noindent I prefer\hspace{2cm} $\Box$ single room\hspace{2cm}$\Box$ double room\\ \hspace{1cm}I would like to share the room with\ \dotfill\\ \bigskip \noindent Special meal requirements (please specify): \dotfill\\ \bigskip \noindent I will arrive \dotfill\\ I will depart \dotfill\\ I am a member of IFIP WG 14.3 \ \ \ $\Box$ yes \ \ $\Box$ no\\ \bigskip \noindent \begin{tabular}{@{}lll}\multicolumn{3}{@{}l@{}}{\hspace*{\textwidth}}\\[0em] Name of accompanying non-participants &\multicolumn{2}{l@{}}{\dotfill} \\ \multicolumn{1}{r}{for which I need} &\ldots\ldots\ldots& additional single rooms and \\ &\ldots\ldots\ldots& additional double rooms \end{tabular} \vfill \hspace{5cm}Signature \dotfill \end{document}

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None
by Jaap van Oosten 22 Nov '94

22 Nov '94

The 56th Peripatetic Seminar on Sheaves and Logic will be held in Aarhus, in the weekend of 3-4 December, 1994. Should people still wish to register and avail themselves of relatively cheap accomodation (around 25 British Pounds per night), it is imperative that I receive their registrations before MONDAY November 28, at noon. Hoping to see you in Aarhus, Jaap van Oosten

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whoops ...
by Michael Makkai 19 Nov '94

19 Nov '94

Today (November 18th), a certain (essentially unknown) number of messages that have arrived since yesterday afternoon got erased from my mailfile before I had a chance of reading them. So, if you have made a request concerning the two papers I recently announced, and if you have not received on e-mail an acknowledgement from me, then please repeat your request. Sorry for the inconvenience. Cheers: Michael Makkai

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processes and irredundant trees
by Dusko Pavlovic 18 Nov '94

18 Nov '94

The promised companion to the paper I announced last week is now available. The first version, which I gave to some people, actually CONTAINED AN ERROR --- so please download this version if you have an old copy. The file is CCPS.ps, and can be downloaded either from triples.math.mcgill.ca, or from theory.doc.ic.ac.uk. Regards, -- Dusko CONVENIENT CATEGORIES OF PROCESSES AND SIMULATIONS by Dusko Pavlovic Abstract. We show that irredundant trees, used by Dana Scott in the early sixties, can be used as canonical representants of the bisimilarity classes of automata (or of transition systems). Simulations then boil down to tree morphisms. Along the same lines, the categories of processes modulo the observational and the branching congruences, with the suitable simulations as morphisms again, are shown to be isomorphic with certain subcategories of the category of irredundant trees.

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The categorical theory generated by a limit sketch
by Charles F. Wells 17 Nov '94

17 Nov '94

About two weeks ago I announced the availability of a paper The categorical theory generated by a limit sketch by Michael Barr and Charles Wells by gopher from gopher.cwru.edu and by ftp from ftp.cwru.edu. I have discovered that the copy I posted was not the latest version. The latest version has now been posted. The differences are correction of a few minor errors plus some additional references. -- Charles Wells, Department of Mathematics, Case Western Reserve University 10900 Euclid Avenue, Cleveland OH 44106-7058, USA Phone 216 368 2880 or 216 774 1926 FAX 216 368 5163

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Availability of new paper by ftp
by Max Kelly 16 Nov '94

16 Nov '94

A new preprint "On localization and stabilization for factorization systems", by Carboni, Janelidze, Kelly, and Pare', is available in our ftp site at the address maths.su.oz.au (= 129.78.68.2), in the directory sydcat/papers/kelly, under the titles cjkp.dvi or cjkp.ps; there is also cjkp.tex, but that requires two macros - namely diagrams.tex and kluwer.sty. The paper contains new ideas, but also self-contained introductions to several areas with which some may be unfamiliar: namely factorization systems, descent theory, Galois theory, Eilenberg's monotone-light factorization for maps between compact hausdorff spaces, hereditary torsion theories for abelian categories, the category of finite families of objects of a given category, and the (separable, purely-inseparable) factorization for field extensions. What ways are there of constructing a factorization system (E, M) on a category C ? One simple one is to start with a full reflective subcategory X of C, and to take E to consist of the maps inverted by the reflexion. Of course, this (E, M) doesn't have E pullback-stable except in the special case where X is a LOCALIZATION of C. We examine another general process, which leads to an (E, M) with E stable when it succeeds. We start from ANY factorization system (E, M), and define new classes thus: a map lies in E' if EACH of its pullbacks lies in E; and it lies in M* if SOME pullback of it along an effective descent map lies in M. Note the connexion with Galois theory, in Janelidze's categorical formulation of it: if the (E, M) we begin with arises as above from a reflective full subcategory, the class M* consists of what Janelidze calls the COVERINGS (or, in some contexts, the CENTRAL EXTENSIONS). It is not always the case that (E', M*) is a factorization system; we give necessary and sufficient conditions for it to be so, and apply these to three major examples: Eilenberg's factorization above, certain factorizations connected to hereditary torsion theories, and a new factorization system for finite-dimensional algebras over a field that generalizes (separable, purely-inseparable) factorization for field extensions. Regards to all - Max Kelly. ps: For those without electronic access, a limited number of printed copies will shortly be available; please request them soon, so that we can alert the printer. Max Kelly.

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