From mboxrd@z Thu Jan 1 00:00:00 1970 X-Msuck: nntp://news.gmane.io/gmane.science.mathematics.categories/4576 Path: news.gmane.org!not-for-mail From: "George Janelidze" Newsgroups: gmane.science.mathematics.categories Subject: Non-cartesian categorical algebra Date: Sun, 14 Sep 2008 15:39:11 +0200 Message-ID: NNTP-Posting-Host: main.gmane.org Mime-Version: 1.0 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: 7bit X-Trace: ger.gmane.org 1241020037 13910 80.91.229.2 (29 Apr 2009 15:47:17 GMT) X-Complaints-To: usenet@ger.gmane.org NNTP-Posting-Date: Wed, 29 Apr 2009 15:47:17 +0000 (UTC) To: Categories Original-X-From: rrosebru@mta.ca Sun Sep 14 13:59:43 2008 -0300 Return-path: Envelope-to: categories-list@mta.ca Delivery-date: Sun, 14 Sep 2008 13:59:43 -0300 Original-Received: from Majordom by mailserv.mta.ca with local (Exim 4.61) (envelope-from ) id 1Keurs-00074B-Jq for categories-list@mta.ca; Sun, 14 Sep 2008 13:54:36 -0300 Original-Sender: cat-dist@mta.ca Precedence: bulk X-Keywords: X-UID: 46 Original-Lines: 49 Xref: news.gmane.org gmane.science.mathematics.categories:4576 Archived-At: Dear Colleagues, I would like to make a remark concerning my CT2008 talk. First let me recall: A lot of mathematics (e.g. of Galois theory) can be done in the context of adjoint functors between abstract categories with finite limits - and since one gets all finite limits our of finite products and equalizers, one can try a further generalization with monoidal structure plus equalizers. The point was that this seemingly primitive old idea actually works very seriously and should be taken as the idea of developing non-cartesian categorical algebra. And "non-cartesian" is the right idea of "non-commutative" and "quantum", although what Ross Street means by "quantum" is more involved and also important. In particular non-cartesian internal categories are to be taken seriously. At the end of my talk Jeff Egger told us that he knows someone studied such generalized internal categories, and later sent me an email with the name: Marcelo Aguiar; and gave the home page address http://www.math.tamu.edu/~maguiar/ , and... I realized that it is the third time I am informed about this work! Recently (winter 2007) I spend two very nice months in Warsaw invited by Piotr Hajac, and discussing mathematics with him, Tomasz Brzezinski, Tomasz Maszczyk, and a few others - and, among other interesting things, Tomasz Brzezinski showed me Marcelo Aguiar's website, including PhD, where those generalized internal categories were studied. I also recall now an email message from Steven Chase (from 2002) where he mentions "...the notion of a category internal to a monoidal category which was developed by my former doctoral student, Marcelo Aguiar, in his thesis, "Internal Categories and Quantum Groups" (available on line...". In fact the whole story begins, in some sense, with the book [S. U. Chase and M. E. Sweedler, Hopf algebras and Galois theory, Lecture Notes in Mathematics 97, Springer 1969], which does not use monoidal categories yet, but very clearly shows that the commutative case is much easier (for Galois theory) because it makes tensor product (of algebras) (co)cartesian. There are many other important further contributions by other authors of different generations. Knowing them personally, I can name Bodo Pareigis, Stefaan Caenepeel, Peter Schauenburg, and the aforementioned Polish mathematicians (although Tomasz Brzezinski is in UK now), but I am not ready to give any reasonably complete list. There are also things-to-be-corrected happening: for instance by far not enough comparisons have been made with the Australian work on abstract monoidal categories, and some authors use words like "coring"... George Janelidze