From cat-dist Sun May 4 22:37:34 1997 Received: by mailserv.mta.ca; id AA09987; Sun, 4 May 1997 22:32:55 -0300 Date: Sun, 4 May 1997 22:32:55 -0300 (ADT) From: categories To: categories Subject: Ad Message-Id: Mime-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Status: RO X-Status: Date: Sun, 4 May 1997 13:55:31 -0400 From: Michael Barr The Categories Team at McGill and at the University of Ottawa invites applications for Postdoctoral Fellowship. This opening is subject to the availability of government funds (which have been awarded by the granting agency, but not yet appropriated by the legislature). The salary is CA$30,000, and it may be supplemented by a part-time teaching post at McGill. It is a two year limited term appointment. There is no nationality restriction, but the successful candidate will have to go through Canadian and Quebec immigration procedures. Interested candidates should apply, with a CV and a statement of plans, as soon as possible, but not later than the end of May, and should ask for letters from three referees. Candidates interested in teaching should also provide evidence of teaching experience as well as English proficiency if that is not their native language. Written applications and letters of reference will be accepted, but electronic ones are preferred. This notice will also be posted to our web page which may be found at The members of the Categories Team are: M. Barr (McGill), R. Blute (Ottawa), M. Bunge (McGill), T. Fox (Vanier Col.), J. Lambek (McGill), M. Makkai (McGill), A. Sangalli (Champlain Col.), P. Scott (Ottawa), R. Seely (John Abbott Col.). Michael Barr barr@math.mcgill.ca Department of Mathematics and Statistics McGill University 805 Sherbrooke St. W Montreal, QC Canada H3P 1S4 From cat-dist Tue May 6 10:27:09 1997 Received: by mailserv.mta.ca; id AA05796; Tue, 6 May 1997 10:25:41 -0300 Date: Tue, 6 May 1997 10:25:40 -0300 (ADT) From: categories To: categories Subject: cfp: Mathematics of Program Construction '98 Message-Id: Mime-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Content-Transfer-Encoding: QUOTED-PRINTABLE Status: O X-Status: Date: Tue, 06 May 1997 11:26:20 +0200 From: Johan Jeuring MPC '98 Fourth International Conference on=20 MATHEMATICS OF PROGRAM CONSTRUCTION ----------------------------------- http://www.md.chalmers.se/Conf/MPC98/ =20 June 15 - 17, 1998 Marstrand, Sweden CALL FOR PAPERS The general theme of this series of conferences is the use of crisp, clear mathematics in the discovery and design of algorithms and in the development of corresponding software or hardware. The conference theme reflects the growing interest in formal, mathematically based methods for the construction of software and hardware. The goal of the MPC conferences is to report on and significantly advance the state of the art in this area. Previous conferences were held in 1989 at Twente, The Netherlands, organised by the Rijksuniversiteit Groningen, in 1992 at Oxford, United Kingdom, and in 1995 at Kloster Irsee, Germany, organised by Augsburg University. TOPICS The emphasis is on the combination of c o n c i s e n e s s and=20 p r e c i s i o n in c a l c u l a t i o n a l t e c h n i q u e s=20 for program construction. We solicit high quality papers on original research, typically in one of the following areas: - formal specification of sequential and concurrent programs; - constructing implementations to meet specifications; in particular, - program transformation; - program analysis; - program verification; - convincing case studies. While this list is not exclusive it is intended to show the focus of the conference. We expect to publish the proceedings as a Springer LNCS, ready at the conference. VENUE Marstrand is a small island on the beautiful westcoast of Sweden, 40 km from G=F6teborg. The charming old houses, the fortress, the walking paths, and the absence of cars make this island a very pleasant resort. There are direct flights to G=F6teborg Landvetter from most European main cities, and busses from G=F6teborg to Marstrand. SUBMISSION =20 Full papers should be submitted in Postscript format by e-mail to reach Johan Jeuring by December 15, 1997. The details of the submission procedure can be found at http://www.md.chalmers.se/Conf/MPC98/how_to_submit.html=20 Although there is no page limit, submissions should strive for brevity.=20 PROGRAMME COMMITTEE=20 Ralph-Johan Back Finland =20 Roland Backhouse The Netherlands =20 Richard Bird UK =20 Eerke Boiten UK =20 Dave Carrington Australia =20 Robin Cockett Canada =20 David Gries USA =20 Lindsay Groves New Zealand=20 Wim Hesselink The Netherlands=20 Zhenjiang Hu Japan=20 Barry Jay Australia=20 Johan Jeuring Sweden (Chair)=20 Dick Kieburtz USA =20 Christian Lengauer Germany =20 Lambert Meertens The Netherlands =20 Sigurd Meldal Norway =20 Bernhard M=F6ller Germany Chris Okasaki USA=20 Jose Oliveira Portugal Ross Paterson UK =20 Mary Sheeran Sweden =20 Doug Smith USA =20 LOCAL ORGANISATION MPC '98 is organised by the Computing Science department of Chalmers University of Technology and University of G=F6teborg. The organisation committee consists of the following people: Patrik Jansson Johan Jeuring Marie Larsson Mary Sheeran IMPORTANT DATES Submission December 15, 1997 Notification February 9, 1998 Final version due March 30, 1998 POST-CONFERENCE WORKSHOPS The following one-day workshops are being organised in conjunction with=20 MPC '98 and will take place immediately after the main conference. * International Workshop on Generic Programming.=20 * International Workshop on Constructive Methods for Parallel Programming,=20 CMPP'98.=20 CORRESPONDENCE Johan Jeuring (MPC '98) Department of Computing Science Chalmers University of Technology S-412 96 G=F6teborg Sweden E-mail: mpc98@cs.chalmers.se Fax: +46 31 165655 From cat-dist Tue May 6 10:27:10 1997 Received: by mailserv.mta.ca; id AA05870; Tue, 6 May 1997 10:27:07 -0300 Date: Tue, 6 May 1997 10:27:07 -0300 (ADT) From: categories To: categories Subject: Ad (correction) Message-Id: Mime-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Status: O X-Status: [ Please note the correction to the postal code in the last line.] Date: Sun, 4 May 1997 13:55:31 -0400 From: Michael Barr The Categories Team at McGill and at the University of Ottawa invites applications for Postdoctoral Fellowship. This opening is subject to the availability of government funds (which have been awarded by the granting agency, but not yet appropriated by the legislature). The salary is CA$30,000, and it may be supplemented by a part-time teaching post at McGill. It is a two year limited term appointment. There is no nationality restriction, but the successful candidate will have to go through Canadian and Quebec immigration procedures. Interested candidates should apply, with a CV and a statement of plans, as soon as possible, but not later than the end of May, and should ask for letters from three referees. Candidates interested in teaching should also provide evidence of teaching experience as well as English proficiency if that is not their native language. Written applications and letters of reference will be accepted, but electronic ones are preferred. This notice will also be posted to our web page which may be found at The members of the Categories Team are: M. Barr (McGill), R. Blute (Ottawa), M. Bunge (McGill), T. Fox (Vanier Col.), J. Lambek (McGill), M. Makkai (McGill), A. Sangalli (Champlain Col.), P. Scott (Ottawa), R. Seely (John Abbott Col.). Michael Barr barr@math.mcgill.ca Department of Mathematics and Statistics McGill University 805 Sherbrooke St. W Montreal, QC Canada H3A 2K6 ^^^^^^^ From cat-dist Tue May 6 17:16:28 1997 Received: by mailserv.mta.ca; id AA29108; Tue, 6 May 1997 17:15:34 -0300 Date: Tue, 6 May 1997 17:15:34 -0300 (ADT) From: categories To: categories Subject: Re: Change of address Message-Id: Mime-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Status: RO X-Status: Date: Tue, 6 May 1997 15:52:25 -0400 (EDT) From: John Rr Isbell John Isbell is now at ji2@acsu.buffalo.edu. email sent to the old address is supposed to be forwarded. Thanx, John From cat-dist Thu May 8 13:18:19 1997 Received: by mailserv.mta.ca; id AA08899; Thu, 8 May 1997 13:16:23 -0300 Date: Thu, 8 May 1997 13:16:23 -0300 (ADT) From: categories To: categories Subject: Change of Address Message-Id: Mime-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Status: O X-Status: Date: Wed, 7 May 1997 07:13:21 +0100 From: John Duskin John Duskin is now at . e-mail sent to the old address is supposed to be forwarded to this new improved address. Thanx, Jack From cat-dist Fri May 9 13:13:35 1997 Received: by mailserv.mta.ca; id AA20359; Fri, 9 May 1997 13:11:56 -0300 Date: Fri, 9 May 1997 13:11:56 -0300 (ADT) From: categories To: categories Subject: injectivity Message-Id: Mime-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Status: RO X-Status: Date: Fri, 9 May 1997 15:30:53 +0200 (MET DST) From: Marek Golasinski Dear Colleagues, Let $Vect_k$ be the category of vector spaces over a field $k$ and $I$ a small category. Consider the category $I-Vect_k$ of all covariant functors from $I$ to $Vect_k$. For two object $F,F'$ of the category $I-Vect_k$ consider their tensor product $F\otimes F'$ such that $(F\otimes F')(i)=F(i)\otimes F'(i)$ for all $i\in I$ and in the obvious way on the morphisms of $I$. 1) Is it true that this tensor product $F\otimes F'$ is injective provided that $F$ and $F'$ are injective? I am really intersted in its particular case. Namely, let $G$ be a finite group and $O(G)$ the finite associated category of canonical orbits. Objects of $O(G)$ are given by the finite $G$-sets $G/H$ for all subgroups $H\subsetq G$ and morphisms by eqivariant maps. 2) What about preserving the injectivity by the above defined tensor product in the functor category $O(G)-Vect_k$? If that is not true for $I=O(G)$ then I would greatly appreciate getting a counterexample. Many thanks in advance for your kind attention on the problem above. With my best regards, Marek Golasinski From cat-dist Thu May 15 22:20:36 1997 Received: by mailserv.mta.ca; id AA26565; Thu, 15 May 1997 22:17:58 -0300 Date: Thu, 15 May 1997 22:17:58 -0300 (ADT) From: categories To: categories Subject: Re: injectivity Message-Id: Mime-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Status: O X-Status: Date: Tue, 13 May 1997 17:52:00 -0400 From: Michael Barr I have given some thought to this question. I do not have a complete answer, but no one else has posted anything, so I will give what I have. First off, the functor category [I,Vect_k] is an AB5 category with a projective generator and hence a module category. In the particular case that I is the orbits of a group, finite or not, it is just k[G] modules. Now if k is finite, then k[G] is semisimple, whence all modules are injective, unless char(k) | #(G), the so-called modular case. In that case, I haven't worked out the details, but I think the tensor product of finite-dimensional injectives is injective. The argument uses duality in k. In fact, the category is self dual (a *-autonomous category). On the other hand, I think it unlikely that this is true for infinite dimensional spaces, but I do not have a counter-example. There are categories, for instance Ab, in which the tensor product of injectives is injective. The reason for Ab is that every injective is a direct sum of indecomposable injectives and the only non-zero tensor product of indecomposable injectives is Q tensor Q = Q. ================================================ >From cat-dist@mailserv.mta.ca Fri May 9 12:19:50 1997 Received: from Math.McGill.CA (Gauss.Math.McGill.CA [132.206.150.3]) by triples.math.mcgill.ca (8.6.8/8.6.6) with SMTP id MAA04846; Fri, 9 May 1997 12:19:46 -0400 Received: from mailserv.mta.ca ([138.73.102.50]) by Math.McGill.CA (4.1/SMI-4.1) id AA21821; Fri, 9 May 97 12:24:36 EDT Received: by mailserv.mta.ca; id AA20359; Fri, 9 May 1997 13:11:56 -0300 Date: Fri, 9 May 1997 13:11:56 -0300 (ADT) From: categories To: categories Subject: injectivity Message-Id: Mime-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Status: RO Date: Fri, 9 May 1997 15:30:53 +0200 (MET DST) From: Marek Golasinski Dear Colleagues, Let $Vect_k$ be the category of vector spaces over a field $k$ and $I$ a small category. Consider the category $I-Vect_k$ of all covariant functors from $I$ to $Vect_k$. For two object $F,F'$ of the category $I-Vect_k$ consider their tensor product $F\otimes F'$ such that $(F\otimes F')(i)=F(i)\otimes F'(i)$ for all $i\in I$ and in the obvious way on the morphisms of $I$. 1) Is it true that this tensor product $F\otimes F'$ is injective provided that $F$ and $F'$ are injective? I am really intersted in its particular case. Namely, let $G$ be a finite group and $O(G)$ the finite associated category of canonical orbits. Objects of $O(G)$ are given by the finite $G$-sets $G/H$ for all subgroups $H\subsetq G$ and morphisms by eqivariant maps. 2) What about preserving the injectivity by the above defined tensor product in the functor category $O(G)-Vect_k$? If that is not true for $I=O(G)$ then I would greatly appreciate getting a counterexample. Many thanks in advance for your kind attention on the problem above. With my best regards, Marek Golasinski From cat-dist Thu May 15 22:20:37 1997 Received: by mailserv.mta.ca; id AA08322; Thu, 15 May 1997 22:18:45 -0300 Date: Thu, 15 May 1997 22:18:45 -0300 (ADT) From: categories To: categories Subject: An introduction to n-categories Message-Id: Mime-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Status: O X-Status: Date: Tue, 13 May 1997 17:29:58 -0700 (PDT) From: john baez Here is the abstract of a paper that is now available in Postscript form at: http://math.ucr.edu/home/baez/ncat.ps If downloading it or printing it out is a problem, I can mail copies to people. ---------------------------------------------------------------------- An Introduction to n-Categories John C. Baez An n-category is some sort of algebraic structure consisting of objects, morphisms between objects, 2-morphisms between morphisms, and so on up to n-morphisms, together with various ways of composing them. We survey various concepts of n-category, with an emphasis on `weak' n-categories, in which all rules governing the composition of j-morphisms hold only up to equivalence. (An n-morphism is an equivalence if it is invertible, while a j-morphism for j < n is an equivalence if it is invertible up to a (j+1)-morphism that is an equivalence.) We discuss applications of weak n-categories to various subjects including homotopy theory and topological quantum field theory, and review the definition of weak n-category recently proposed by Dolan and the author. From cat-dist Thu May 15 22:20:37 1997 Received: by mailserv.mta.ca; id AA26557; Thu, 15 May 1997 22:19:35 -0300 Date: Thu, 15 May 1997 22:19:35 -0300 (ADT) From: categories To: categories Subject: correction Message-Id: Mime-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Status: O X-Status: Date: Thu, 15 May 1997 10:12:30 +0200 (MET DST) From: Jiri Rosicky At the 64th PSSL at Braunschweig, I gave a talk about cartesian closedness of exact completions with an intention to cover equilogical spaces in the sense of Dana Scott (see D.S.Scott, A New category? Domains, Spaces and Equivalence Relations, preprint 1996). Unfortunately, Peter Johnstone found a flaw in my argument. I would like to announce the following result which covers equilogical spaces: Theorem: Let C be an infinitary extensive category. Then its exact completion ex(C) is cartesian closed iff C is weakly cartesian closed. Moreover, the embedding C-->ex(C) preserves exponentials. From cat-dist Sun May 18 17:47:48 1997 Received: by mailserv.mta.ca; id AA14922; Sun, 18 May 1997 17:46:53 -0300 Date: Sun, 18 May 1997 17:46:53 -0300 (ADT) From: categories To: categories Subject: Final CFP: Third Special Australasian Issue of Theoretical Computer Science Message-Id: Mime-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Status: O X-Status: Date: Tue, 13 May 1997 14:14:34 +1000 From: James Harland [Apologies if you receive multiple copies of this announcement.] Third Special Australasian Issue of Theoretical Computer Science ---------------------------------------------------------------- Call for Papers ---------------- The recent CATS'97 meeting in Sydney endorsed arrangements for a third special issue of the journal "Theoretical Computer Science" (TCS) devoted to work by anyone connected to Australia or New Zealand in some way. This includes expanded versions of papers presented at CATS'97, or some other recent and relevant conference in Australia or New Zealand, or papers of which at least one author is resident in Australia or New Zealand. The submission criteria are the same as for normal TCS papers, and can be found in any recent issue of TCS. If it should happen that there are more acceptable papers than can appear in the special issue, then the excess will appear in a regular issue of the journal. The deadline for submissions is 31st May, 1997. Papers should be submitted to: James Harland Department of Computer Science Royal Melbourne Institute of Technology GPO Box 2476V Melbourne, 3001 Victoria, Australia (e-mail jah@cs.rmit.edu.au) Please forward to any interested parties, not already listed. From cat-dist Sun May 18 17:47:59 1997 Received: by mailserv.mta.ca; id AA13944; Sun, 18 May 1997 17:47:58 -0300 Date: Sun, 18 May 1997 17:47:58 -0300 (ADT) From: categories To: categories Subject: CT97 Message-Id: Mime-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Status: RO X-Status: Date: Fri, 16 May 97 16:50:56 -0700 From: John MacDonald LAST CALL FOR PREREGISTRATION INTERNATIONAL CATEGORY THEORY MEETING (CT97) July 13-19, 1997 University of British Columbia Vancouver, Canada The conference arrival day is Sunday July 13 with a reception 6-9pm in the Fireplace Lounge of Walter Gage Towers on the UBC campus. The scientific program will begin Monday morning July 14 at 9am in Angus 104 and will finish on Saturday July 19 at the end of the morning session (12:30pm). On Wednesday afternoon July 16 there will be a Vancouver city tour followed by a dinner cruise with Harbour Ferries. Pickup time will be 2:30pm in front of Gage Towers. On Friday evening there will be a banquet starting at 7:30PM. PREREGISTRATION If you plan to attend the conference and have not preregistered, or if you would like more information to enable you to decide whether to attend, then please preregister as soon as possible. To preregister, and thus receive future announcements as well as a registration form and a housing form please send e-mail to johnm@math.ubc.ca with subject `preregistration'. Please provide your name and a postal address in the body of the message. HOUSING DEADLINE Accomodation is available on the U.B.C. campus in a block of rooms being held for CT97 until June 13, one month before the starting date of the conference. On June 13 all rooms from our block which have not been individually reserved will be released to the public for reservation. After this time one can still request space on an individual basis, but the outcome is less certain, especially since a major music festival begins in Vancouver on July 18. If you think that you may attend but are not sure yet, then you may find it advisable to reserve a room since this can be done by email on the housing form and for the single rooms with shared washroom it does not require a deposit. If you have preregistered but have misplaced your room reservation form, then please send email to johnm@math.ubc.ca with the subject Housing and a room reservation form will be sent to you. TALK DEADLINE If you wish to give a talk and have not yet informed the organizers, then please let us know of your intention by May 31 by sending email to johnm@math.ubc.ca including a title, if possible. Abstracts should be sent to stone@math.ubc.ca by June 10. There may be parallel sessions on some afternoons. The total number of speakers may have to be limited as well. PREREGISTRANT LIST For your information a list of those who have preregistered as of May 16 is attached. This list is presented roughly in the order in which preregistrations were received. If your name is not on the list and you would like it added, then please follow the procedure listed under PREREGISTRATION above. CT97 PREREGISTRATION LIST (5/16/97) P.J. Johnstone, C.J. Mulvey, M. Hebert, M. Grandis, R.J. Wood B. Jay, S. Niefeld, J. Isbell, D. Novick, F. Gago I. Moerdijk, J. Funk, F. Zalamea, H. Lord, H. Hu J. Duskin, Y. Katsov, H. Marcum, J.R. Otto, M. Johnson R. Pare, P. McCrudden, H.E. Porst, R. Seely, R. Gates V. Pratt, R. Kieboom, J. Rosicky, G. Rosolini, S. Crans R. Street, S. Lack, U. Montanari, F. Piessens, W. Hunsaker F.W. Lawvere, H. Kleisli, J.W. Pelletier, L.S. Barbosa, P.C. Carrasco W. Tholen, A. Madanshekaf, J. Picado, F. Marmolejo, S. Fusco Y.P. Velinov, R. Rosebrugh, A. Schauerte, W. Boshuck, D. Bourn S. Mac Lane, J. MacDonald, A.Stone, L. Roman, S. Mantovani G.M. Kelly, L. Mauri, C. Pedicchio, J. Thiessen, M. Thiebaud M. Barr, G. Richter, F.G. Lastaria, D. Hofmann, J. Walters-Wayland L. Sousa, M.J.Healy, P. Mulry, R. Dawson, Z. Omiadze J. Koslowski, F. Linton, D. Pronk, A. Kock, H. Miyoshi C. Hermida, D. Schumacher From cat-dist Mon May 19 09:20:02 1997 Received: by mailserv.mta.ca; id AA29906; Mon, 19 May 1997 09:19:25 -0300 Date: Mon, 19 May 1997 09:19:25 -0300 (ADT) From: categories To: categories Subject: Scott is Phoa, locally Message-Id: Mime-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Status: O X-Status: Date: Mon, 19 May 1997 13:29:05 MESZ From: Thomas Streicher In a paper circulated since end of last year Dana Scott has proposed a category PEQU of algebraic lattices with partial equivalence relations as objects and equivariant Scott continuous maps as morphisms. One nice thing about PEQU is that Scott has shown it to be equivalent to the category EQU of T_0 spaces with (total) equivalence relations and equivariant continuous maps. It has been shown (by students of Scott) that PEQU is not even well-powered despite being regular and locally cartesian closed (in particular, it is a logos and thus a model for FOL). If one considers $\omega$-PEQU, the category of $\omega$-algebraic lattices with partial equivalence relations as objects and equivariant Scott continuous maps as morphisms, then it can be shown easily to be equivalent to PER(P $\omega$), the category of pers over the good old P $\omega$ model of lambda calculus, which embeds into Ass(P $\omega$), the category of assemblies over P $\omega$ and finally into RT(P $\omega$), the realisability topos over P $\omega$. All these full inclusions are reflective. This realisability model has been studied by Wesley Phoa in his Thesis (1990) and in his paper "Building Domains from Graph Models" (MSCS, 1992). The reason for the equivalence of $\omega$-PEQU and PER(P $\omega$) is that any $\omega$-algebraic lattice L is contained in P $\omega$ via an inflationary retract e : L -> P $\omega$ , p : P $\omega$ -> L. Now if R is a per on L then P $\omega$ may be endowed with the per e[R] := { (e(x),e(y)) | x R y } and the pair e,p of equivariant Scott continuous maps establishes an isomorphism between (L,R) and (P $\omega$ , e[R]). This observation does not hinge on countable cardinality. For any cardinal $\kappa$ we may consider $\kappa$-PEQU (where the bases of the algebraic lattices are required to have cardinality less or equal $\kappa$) and show it to be equivalent to PER(P $\kappa$) by the same argument as above. The reason why this is possible is that any infinite set M contains List(M) x M as a retract and therefore can be endowed with a graph model structure -- as emphasised by Scott. The benefits of this (simple) observation are the following (1) $\kappa$-PEQU does not admit a generic (regular) mono (= weak s.o. classifier) as for any partial combinatory algebra A the category PER(A) does not admit such (as each homset has cardinality less or equal |A| and there are 2^{|A|} (regular) subobjects of (A, \Delta(A))) but, never mind, the required weak / strong classifiers live in Ass(A) / RT(A) , respectively (2) Phoa already has started to investigate SDT in PER(P $\omega$), one may take as a dominance (S , \Delta(S)) where S is Sierpinski space together with [t] : ({*} , \Delta({*})) -> (S , \Delta(S)) where t(*) = \top. The same may be taken as a dominance for PEQU without any size restrictions. Anyway, PEQU appears as an amalgamation of ALL realisability models over graph models of all size. Assuming a Grothendieck universe U we may consider (the fairly big) graph model P U appearing most naturally so as we have List(U) x U \subseteq U. Thus PER(P U) contains PEQU, i.e. EQU, when one restricts the underlying algebraic lattices / T_0 spaces of PEQU / EQU to live in universe U. But notice that (P U , \Delta(P U)) lives outside this PEQU. Anyway, PER(P U), Ass(P U), RT(P U) appear as the appropriate models of logic in which to study Scott's recently proposed categories. >From the point of view of mathematical practice, however, the restriction to cardinality $\omega$ does not seem to be too restrictive as most spaces in "real" mathematics have a countable base (e.g. separable metric spaces). Thomas Streicher From cat-dist Tue May 20 21:18:48 1997 Received: by mailserv.mta.ca; id AA29120; Tue, 20 May 1997 21:18:10 -0300 Date: Tue, 20 May 1997 21:18:10 -0300 (ADT) From: categories To: categories Subject: ANNOUNCING: Xy-pic version 3.4 released! Message-Id: Mime-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Status: O X-Status: Date: Tue, 20 May 1997 16:19:28 +0200 (MET DST) From: Kristoffer Hogsbro Rose Dear Category Theorists, Please find enclosed a copy of the TRAILER for a new version of Xy-pic. I hope you will find it useful. Notice that DIKU has discontinued my ftp directory, so the principal home of Xy-pic is now at brics.dk. Sincerely, Kristoffer H. Rose ======================================================================= ANNOUNCING the Xy-pic version 3.4 DIAGRAM TYPESETTING PACKAGE ======================================================================= This is to announce a RELEASE of the DIAGRAM TYPESETTING PACKAGE: Xy-pic 3.4 This is a maintenance release where a few more bugs of the previous major release of Xy-pic 3 have been eliminated and a few things have been added... ----------------------------------------------------------------------- GENERAL ----------------------------------------------------------------------- Xy-pic is a package for typesetting a variety of graphs and diagrams with TeX. Xy-pic works with most formats (including LaTeX, AMS-LaTeX, AMS-TeX, and plain TeX), in particular Xy-pic is provided as a LaTeX2e `supported package' (following the `CTAN LaTeX2e bundle' standard). Further specifics of the package are in the distribution README file. ----------------------------------------------------------------------- NEWS ----------------------------------------------------------------------- Xy-pic version 3 was a thorough rewrite of the prior major version, version 2 (last version 2 release was release 2.6; several beta-test releases of version 3, numbered 2.7-2.12, were made available to users). However, full backwards compatibility is maintained (except for the unavoidable but fully documented obscure cases). Release 3.4 fixes the following problems remaining in release 3.3: * \txt and v2 arrow commands now work again, even first in matrix entries! * Tiling patterns are functional again! * PostScript frames have the right shape again! * The [F**] `enhance' modifier is now useful, even without PostScript! * Using Xy-constructions with & inside other table constructs possible! * Improved non-PostScript curved dashing! * `Illegal parameter number in definition of \lastprentry@@' bug fixed! as well as the usual collection of minor fixes in code & documentation (all described in the ChangeLog file of the source distribution). Thanks to J|rgen Koslowski, Clemens Beckstein, G. Allen Morris III, Chris L. Skeels, and Peter Selinger, for your bug reports (and to David Carlisle for reminding us of LaTeX2e's \AtBeginDvi mechanism, and last but not least to Karl Berry for releasing web2c-7.0 so we won't have to get `out of memory' errors any more and gee are we proud of being the only macro package mentioned in texmf.cnf :) ----------------------------------------------------------------------- AVAILABILITY ----------------------------------------------------------------------- Xy-pic can be retrieved through the World Wide Web Xy-pic `home pages': URL: http://www.brics.dk/~krisrose/Xy-pic.html URL: http://www.mpce.mq.edu.au/~ross/Xy-pic.html as well as by anonymous ftp from CTAN: macros/generic/diagrams/xypic and from the private archives of the authors: ftp.brics.dk : /Staff/krisrose/TeX/ ftp.mpce.mq.edu.au : /pub/maths/TeX/ Check the README file in each location for specifics. ----------------------------------------------------------------------- HISTORY & CREDITS ----------------------------------------------------------------------- The first public release (version 1.40) of Xy-pic was created by Kristoffer H. Rose, DIKU, U of Copenhagen (now BRICS, U of Aarhus) and distributed via Usenet on December 19, 1991. (Version 3.3 was released on December 19, 1996 because this was the fifth anniversary of Xy-pic.) This quickly became Version 2 of which version 2.6 was the most stable. The rewrite that became version 3 is a continued collaboration with Ross Moore, Macquarie U, Sydney, initiated through a visit to Macquarie (Jan-May 1994 supported by the Australian Research Council, Macquarie University, and using donated DEC equipment). Xy-pic is Copyright (c) 1991-1997 by Kristoffer H. Rose and 1994-1997 by Ross Moore under GNU COPYLEFT which means that you can use the package for any purpose but if you provide the macros or any code derived from them to a third party then you are obliged to include the entire Xy-pic package (full details in the file COPYING). ----------------------------------------------------------------------- This is the end of the announcement. Enjoy Xy-pic! ----------------------------------------------------------------------- PS. Don't miss TUG'97 with the latest in advanced TeX/LaTeX web & math typesetting developments! See -- Kristoffer Hxgsbro ROSE, Ph.D. BRICS International Ph.D. School Department of Computer Science +45 89423193, 20900180, fax 89423255 University of Aarhus, Ny Munkegade, bld. 540, DK-8000 Erhus C, DENMARK From cat-dist Wed May 21 14:03:02 1997 Received: by mailserv.mta.ca; id AA25879; Wed, 21 May 1997 14:03:00 -0300 Date: Wed, 21 May 1997 14:03:00 -0300 (ADT) From: categories To: categories Subject: PhD-Studentships in Theoretical Computer Science Message-Id: Mime-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Status: O X-Status: Date: Wed, 21 May 1997 17:41:34 +0100 From: Eike Ritter THE UNIVERSITY OF BIRMINGHAM SCHOOL OF COMPUTER SCIENCE RESEARCH OPPORTUNITIES IN THEORETICAL COMPUTER SCIENCE The School of Computer Science, broadly grouped into areas of Theory of Computation, Artificial Intelligence, and Software Engineering, offers a number of PhD studentships each year. The Theory of Computation group concentrates on the development of logics and semantics for programming languages. The overall aim is to provide intuitive conceptual tools for the everyday practice of programming. Within this framework, the activities range from abstract mathematics to issues of implementation and software development. Current research projects include probabilistic computation and model checking, semantics for concurrent systems, observation logics, exact real number computation, semantics for databases, (linear) functional programming, type systems for optimization of programs, and automated deduction. Current members of the Theory group are: Dr Valeria de Paiva, Professor Achim Jung, Dr Marta Kwiatkowska, Dr Eike Ritter and Dr Mark Ryan. There are also two Research Fellows (Dr Natasha Alechina and Dr Neil Ghani) and 9 PhD students associated with the group, of the total of 30 in the School. Possible topics for research include, but are not restricted to: Probabilistic and stochastic systems Software verification Semantics for concurrency Extensions to the relational database model (theory and implementation) Semantics of object-oriented languages Linear abstract machines Type systems for imperative and OO programming Machine-assisted reasoning Categorical models of rewriting Applicants should possess a good honours degree (equivalent to an upper second class degree in a UK university) in Mathematics or Computer Science, or a closely related title. Applicants willing to undertake building software systems as part of their research are particularly encouraged. Informal enquiries can be directed to any member of the group: Valeria de Paiva +44 121 414 4766 Achim Jung +44 121 414 4776 Marta Kwiatkowska +44 121 414 7264 Eike Ritter +44 121 414 4772 Mark Ryan +44 121 414 7361 email {vdp,axj,mzk,exr,mdr}@cs.bham.ac.uk Additional information about the School of Computer Science and the University of Birmingham is accessible via WWW from URL: http://www.cs.bham.ac.uk From cat-dist Wed May 21 14:03:05 1997 Received: by mailserv.mta.ca; id AA12313; Wed, 21 May 1997 14:02:05 -0300 Date: Wed, 21 May 1997 14:02:05 -0300 (ADT) From: categories To: categories Subject: Last Call Message-Id: Mime-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Status: O X-Status: Date: Wed, 21 May 1997 11:48:50 -0300 From: ruy@di.ufpe.br 4th Workshop on Logic, Language, Information and Computation (WoLLIC'97) August 20-22 1997 Fortaleza (Ceara'), Brazil LAST CALL FOR CONTRIBUTIONS DEADLINE: 1st of June! http://www.di.ufpe.br/~wollic97 (Sincere apologies apply if you receive multiple copies of this message.) From cat-dist Sat May 24 16:43:05 1997 Received: by mailserv.mta.ca; id AA17375; Sat, 24 May 1997 16:41:31 -0300 Date: Sat, 24 May 1997 16:41:31 -0300 (ADT) From: categories To: categories Subject: BarrFest Schedule Message-Id: Mime-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Status: RO X-Status: Date: Sat, 24 May 1997 09:29:52 -0400 From: Robert A. G. Seely Here is the (reasonably final) schedule of talks for the BarrFest meeting in Montreal May 29 - 31. Details of the meeting (as well as a PS file of the schedule) are available from the Categories (Montreal) group's WWW site - Robert Seely ------------------- Barrfest Schedule May 29-31, 1997 THURSDAY 9:00- 9:55 Murray Gerstenhaber Developments from Barr's thesis 10:00-10:25 George Janelidze On Barr's results on Galois theory in topoi, and further developments from topoi to general categories 11:00-11:55 Fred E J Linton HomB ( B B ) and all that 12:00-12:25 Noson Yanofsky Obstructions to Coherence - Lunch 1:30- 2:25 Jack Duskin Higher Dimensional Non-Abelian Cohomology via Cotriples 2:30- 3:25 Donovan VanOsdol Barr, Cobar, and Koszul 4:00- 4:25 Marta Bunge Admissible KZ-doctrines: overview and examples 4:30- 4:55 Jonathon Funk A bicomma object condition for KZ-doctrines 5:05- 6:00 Jim Lambek Diagram chasing in ordered categories with involution FRIDAY 9:00- 9:55 Saunders MacLane Triples versus Universal Algebra 10:00-10:25 Hongde Hu Coherence completions, free bicompletion and Chu construction 11:00-11:25 Vaughan Pratt Chu Spaces as Universal Algebras 11:30-12:25 Peter Chu Torsion theory in Rings with several objects - Lunch 1:30- 2:25 John Power Sketches 2:30- 3:25 John Kennison Solution manifolds for differential equations 4:00- 4:25 Ieke Moerdijk Barr's covering theorem and coherent Hausdorff topoi 4:30- 4:55 Walter Tholen Functorial factorization, well-pointedness and separability 5:05- 6:00 Myles Tierney 2-torsors, 2-descent, etc 6:45- ? Dinner Thompson House SATURDAY 9:00- 9:55 Charles Wells Graph Based Logic and Equational Logic 10:00-10:25 Dorette Pronk Simplicial Cohomology of Orbifolds 11:00-11:55 James Otto Presenting LCC categories by answering queries 12:00-12:25 Francois Lamarche Chu spaces and denotational semantics - Lunch 1:30- 2:25 Michael Makkai A somewhat personal overview of regular categories 2:30- 2:55 Robin Cockett Montreal summers need not be listless 3:00- 3:25 Robert Seely Linearly distributive functors 4:00- 4:25 Richard Blute Nuclear Ideals in Tensored *-categories 4:30- 4:55 Bernhard Banaschewski A uniform view of real compactness 5:05- 6:00 Peter Freyd Cartesian Logic, Alternation Logic From cat-dist Tue May 27 13:47:54 1997 Received: by mailserv.mta.ca; id AA14388; Tue, 27 May 1997 13:46:19 -0300 Date: Tue, 27 May 1997 13:46:19 -0300 (ADT) From: categories To: categories Subject: equilogical spaces Message-Id: Mime-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Status: RO X-Status: Date: Tue, 27 May 1997 18:35:03 +0200 (MET DST) From: Jiri Rosicky With J.Adamek, we have proved that the category of topological spaces is weakly cartesian closed. Hence its exact completion is cartesian closed (following the result I announced on May 15). From cat-dist Thu May 29 14:35:18 1997 Received: by mailserv.mta.ca; id AA25072; Thu, 29 May 1997 14:33:57 -0300 Date: Thu, 29 May 1997 14:33:57 -0300 (ADT) From: categories To: categories Subject: Re: injectivity Message-Id: Mime-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Status: O X-Status: Date: Wed, 28 May 1997 11:22:00 +0200 From: Dr. Reinhard B/rger (Prof. Dr. Pumpl^nn) Michael Barr mentions the example Ab. There is even an easier reason why tensor products of injectives in Ab are injective and it even injectivity of one factor suffices: Injecitive abelian groups coincide with divisible abelian groups and a tensor product is divisible if one factor is. This holds in a more general sitution, e.g. for modules over a principal ideal domain. It might be worthwile to look for a general (categorical) reason for this phenomenon. Greetings Reinhard Boerger