Robert Pare | 21 Sep 21:16 2014
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Dietmar Schumacher

It is with great sadness that I announce that my longtime friend and collaborator,
Dietmar Schumacher, died on Wednesday September 17, 2014, of a massive stroke.

It was in 1971, when he took up his position at Acadia University, that he left a note
on my office door introducing himself and suggesting we meet to discuss category
theory. We did and that was the start of our long collaboration. We also started, in 1972, 
the category seminar which still runs today, 42 years later. For many years  he would drive
the 100 kms from Wolfville every week to attend the seminar, and drive back  afterwards. 
He would sometimes speak in the seminar or, if not, stimulated discussion with his penetrating 
questions. The last few years, he came less often as he found the drive tiring, but invariably 
he would read up on the topic of the week and always emailed me a question or two about it.
He kept up his interest in category theory until the end. He came to the first seminar this year,
just two weeks ago, looking strong and fit as ever.

We'll miss his wry sense of humour. His way of apologizing for some little thing, and then 
apologizing for apologizing.

Our thoughts are with his family at this difficult time.

Bob

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Edward A. Hirsch | 18 Sep 12:59 2014
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CSR 2015: First Call for Papers

(apologies if you receive multiple copies)

CSR-2015: First Call for Papers

The 10th International Computer Science Symposium in Russia
July 13-17, 2015, Listvyanka (Lake Baikal), Russia
http://logic.pdmi.ras.ru/csr2015
In partnership with European Association for Theoretical Computer Science

Program Committee Chair:
  Lev Beklemishev (Steklov Inst./Moscow)

Program Committee:
  Eric Allender (Rutgers)
  Sergei Artemov (U. of New York)
  Andrei Bulatov (Simon Fraser U.)
  Harry Buhrman (U. of Amsterdam)
  Nachum Dershowitz (Tel Aviv U.)
  Edward A. Hirsch (Steklov Inst./St.Petersburg)
  Bahkadyr Khoussainov (U. of Auckland)
  Gregory Kucherov (CNRS and U. Marne-la-Vallee)
  Sergei O. Kuznetsov (Higher School of Economics/Moscow)
  Daniel Leivant (Indiana U.)
  Georg Moser (U. of Innsbruck)
  Damian Niwinski (U. of Warsaw)
  Prakash Panangaden (McGill U.)
  Jean-??ric Pin (CNRS and U. Paris-Diderot)
  Alexander Razborov (U. of Chicago and Steklov Inst./Moscow)
  Andre Scedrov (U. of Pennsylvania)
  Alexander Shen (LIRMM/Montpellier and IITP/Moscow)
(Continue reading)

Jiri Adamek | 17 Sep 14:59 2014
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papers on colimits of monads available

I would like to announce two papers available on arxiv:

----------------------
J. Adamek, N. Bowler, P. Levy and S. Milius:
Coproducts of Monads on Set (http://arxiv.org/abs/1409.3804)

(This is an abstract, extended by proofs in the appendix, of a talk
presented at LICS 2012.)

A monad M on Set is proved to have a coproduct with every monad in
the category Monad(Set) iff M is a submonad of either the terminal
monad (constant to 1) or an exception monad (sending X to X+E). Calling
such monads trivial, we prove that a coproduct of nontrivial monads
exists iff the monads have arbitrarily large joint pre-fixpoints.
(A pre-fixpoint of an endofunctor M is an object X such that MX is
a subobject of X.) A surprisingly simple formula for coproducts of monads
in Set is presented

--------------------------
J. Adamek: Colimits of Monads (http://arxiv.org/abs/1409.3805)

For "set-like" categories A the category Monad(A) is proved to
have coequalizers. It also has a colimit of every diagram
such that arbitrarily large joint pre-fixpoints of all the monads
exist. This is stronger than the well-known fact that accessible
monads admit all colimits. Somewhat surprisingly, the category of monads
on Gra does not have coequalizers.

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(Continue reading)

Dana Scott | 14 Sep 02:28 2014
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Re: looking for a reference...

If you have comments/suggestions, please reply to Mr. Kruckman.  Thanks.

On Sep 13, 2014, at 10:02 AM, Alex Kruckman <kruckman <at> gmail.com> wrote:

> Professor Scott,
> 
> In writing up some work I did with another graduate student, we’ve
> noticed that one argument is really a special case of a very general
> fact. It's easy to prove, and it's quite nice, but I've never seen it
> explicitly noted. Have you?
> 
> Here it is:
> 
> 1. Suppose we have a contravariant functor F from Sets to some other
> category C which turns coproducts into products. This functor automatically
> has an adjoint, given by G(-) = Hom_C(-,F(1)), where 1 is the one element
> set. If you like, the existence of G is an instance of the special adjoint
> functor theorem, but it's also easy to check by hand. The key thing is that
> every set X can be expressed as the X-indexed coproduct of copies of the one
> element set, so we have (the = signs here are natural isomorphisms):
> 
> Hom_C(A,F(X)) = Hom_C(A,F(coprod_X 1)) = Hom_C(A,prod_X F(1)) =
> 	prod_X Hom_C(A,F(1)) = prod_X G(A) = Hom_Set(X,G(A))
> 
> 2. Now let's say the category C is the category of algebras in some signature.
> Let's call algebras in the image of F "full", and let's say we're interested
> in the class K of subalgebras of full algebras. This class is closed under
> products and subalgebras, so if it's elementary, then it has an axiomatization
> by universal Horn sentences (i.e. it's a quasivariety), and moreover every algebra
> in the class is a subalgebra of a product of copies of F(1), so a universal Horn
(Continue reading)

Dirk Hofmann | 10 Sep 10:40 2014
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CT2015

Dear Colleagues,

this is a very preliminary announcement regarding the next International
Category Theory Meeting CT2015, which will take place in Aveiro,
Portugal, from Sunday, June 14 till Friday, June 19.

Scientific committee:

Martin Hyland - University of Cambridge
George Janelidze - University of Capetown
Joachim Kock - Universitat Aut??noma de Barcelona
Steve Lack - Macquarie University, Sydney
Susan Niefield - Union College, NY
Jiri Rosicky - Masaryk University, Brno
Manuela Sobral - University of Coimbra
Walter Tholen (chair) - York University, Toronto
Richard Wood - Dalhousie University, Halifax

Organising committee:

Gon??alo Gutierres - University of Coimbra
Dirk Hofmann - University of Aveiro
Pedro Nora - University of Aveiro
Jorge Picado - University of Coimbra
Carla Reis - Polytechnic Institute of Coimbra
Ana Helena Roque - University of Aveiro
Jo??o Xarez - University of Aveiro

More information will follow soon in further announcements.

(Continue reading)

Bob Rosebrugh | 5 Sep 02:41 2014
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Refining the function of the Categories List

Dear Colleagues:

For nearly 25 years the categories mailing list has offered announcements,
questions and answers about category theory, and sometimes general discussion.
When the list started in March 1990 email was the only electronic means for
quick, informal exchange.

In the intervening decades the internet has evolved, and there are many
other ways to present and discuss ideas. Forums like mathoverflow,
personal blogs, and group blogs like n-category cafe are much better
venues than a simple text mailing list. They offer formatting, tracking,
permanence and search facilities. It is easy now to begin your own blog on
wordpress or google blogspot.

Until now, the categories list has sometimes posted lengthy back and forth
exchanges. Your moderator has permitted that, at first since there was no
other outlet, and later without thinking about alternatives. Such
exchanges always lead to a number of subscribers leaving the list. Readers
who might have been interested in our subject are driven away. Sometimes,
as moderator, it has also been necessary for me to reject immoderate
messages. Following some rejections I have been insulted, harrassed and
occasionally threatened. Quietly taking that behaviour in stride for the
good of the community was accepted as unpleasant, but necessary.

Recently, another such incident has occurred, though fortunately mostly 
out of view of most of you. That has prompted my determination that the 
list needs its function expressed more precisely so that it can survive in 
the second decade of this century.

Effective immediately, the categories mailing list will continue to post
(Continue reading)

Timothy Revell | 1 Sep 11:12 2014
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Is the category of group actions LCCC?

Dear All,

I'm wondering whether the category of ALL group actions is locally
Cartesian closed. This is NOT the functor category [G,Set] for some
category G with one object, since we allow G to vary. To be more
specific the category is as follows.

  - The objects are pairs (G,X), where G is a group and X is a G-Set.

  - A morphism (G,X) -> (G', X') is given by a pair (h,f), where h:G->G'
is a group homomorphism and f: X -> X' is a function (a morphism in Set)
such that for all  g in G, x in X

    h(g) * f(x) = f(g * x)

where * on the left denotes the group action of G' on X' and * on the
right denotes the group action of G on X.

All the best,
Tim

--

-- 
Timothy Revell,
Department of Computer and Information Sciences,
University of Strathclyde.
The University of Strathclyde is a charitable body, registered in
Scotland, with registration number SC015263.

[For admin and other information see: http://www.mta.ca/~cat-dist/ ]

(Continue reading)

Michael Lambek | 28 Aug 23:43 2014
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celebration of Jim Lambek

Jim Lambek?s family invites you to a celebration of his life

Joachim Lambek
(December 5, 1922 - June 23, 2014)

Saturday, September 20, 2014

12 noon ? 2:00 p.m.

Birks Heritage Chapel
3520 University Street
Montreal, Quebec H3A 2A7
Tel: 514-398-4121
For parking please see:
http://www.mcgill.ca/transport/parking/downtown/wedding-parking

Followed by a reception hosted by the Department of Mathematics

West Room, Victoria College

2:00 ? 5:00 p.m.

Please attend and circulate this invitation to others who may be interested.

We also announce the Jim Lambek Prize in Mathematics to be given annually
to an outstanding mathematics student at McGill with an interest in
linguistics, algebra, logic, or history and philosophy of mathematics.

Should you wish to contribute you may do so in one of 4 ways:
--online: www.mcgill.ca/give  - indicate "Jim Lambek Prize in Mathematics"
(Continue reading)

Toby Bartels | 27 Aug 07:05 2014

Re: Uniform locales in Shv(X)

Jeff Egger <jeffegger <at> yahoo.ca> wrote in part:

>I have an idea of how this might be done, but it requires a detour through gauge spaces [...] which I'm not
sure is constructively valid.

Presumably it's not valid if we don't at least have the classical theorem
that every pointwise uniformity comes from a family of psuedometrics.
The proof that I know of this relies on dependent choice,
as well as forming infima of inhabited sets of nonnegative real numbers.
These infima are constructively valid if we allow our pseudometrics
to take values in the upper real numbers instead of only the real numbers.
I don't know what to do about the dependent choice, however.

--Toby

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henry | 25 Aug 22:24 2014

Re: Uniform locales in Shv(X)

Hi,

My point about the entourage approach was that it does not require
overtness at least for the basic definitions:

For example, you can state the axiom "for all entourage a there exists an
entourage c such that c.c <= a$ as" using the following form instead of
the composition of entourage:

pi_12 ^* c (intersection) pi_23^* c <= pi_13^*a

where pi_12, pi_23 and pi_13 denotes the three projection from X^3 to X^2.

the uniformly below relation can also be defined as: a is uniformly below
b if there exist an entourage c such that pi_1^* a (intersection) c <=
pi_2^* b and hence you can state the admissibility axiom without
overtness.

The absence of overtness still yields a lots of problems: for example the
uniformly below relation is no longer interpolative. (and I agree that it
is not clear at all that this is the good way of doing things)

When focusing on overt space everything work properly and one can defines
for example completeness and completion (it is actually a direct
consequence of the results about localic metric space in my thesis) but at
some point it yields other problems related to the fact that subspaces of
uniform spaces are no longer uniform space and this gives examples of
things that should be uniform spaces but which are not overt.

If you are willing to restrict to open maps then using the entourage
(Continue reading)

Valeria de Paiva | 25 Aug 21:24 2014
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Grigori (Grisha) Mints

Dear colleagues,
I've checked the archives of categories and it seems that the sad news that
Grisha Mints passed away on 29 May 2014 has not reached the community. I am
sad to be the bearer of these news. Richard Zach has a nice post about him (
http://www.ucalgary.ca/rzach/blog/2014/05/grigori-mints-1939-2014.html),
Stanford has a memorial page (
https://philosophy.stanford.edu/content/articles/view/Grisha_Mints_1/) and
his family has a webpage for tributes (http://www.grishamints.net/) I am
missing Grisha very much, a great logician and a great human being.
Valeria

--

-- 
Valeria de Paiva
http://www.cs.bham.ac.uk/~vdp/
http://valeriadepaiva.org/

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Gmane