August 1997 - Categories - categories.org.au

Preprints available
by Walter Tholen 06 Aug '97

06 Aug '97

The following two preprints (joint work with George Janelidze) are available as postscript files from my home page at http://www.math.yorku.ca/Who/Faculty/Tholen/menu.html For titles and abstracts, see below. Walter Tholen -------------------------------------------------------------------------- "Functorial Factorization, Well-pointedness and Separabilty" Abstract: A functorial treatment of factorization structures is presented, under extensive use of well-pointed endofunctors. Actually, so-called weak factorization systems are interpreted as pointed lax indexed endofunctors, and this sheds new light on the correspondence between reflective subcategories and factorization systems. The second part of the paper presents two improtant factorization structures in the context of pointed endofunctors: concordant-dissonant and inseparable-sepaprable. "Extended Galois Theory And Dissonant Morphisms" Abstract: For a given Galois structure on a category C and an effective descent morphism p: E --> B in C we describe the category of so-called weakly split objects over (E,p) in terms of internal actions of the Galois (pre)groupoid of (E,p) with an additional structure. We explain that this generates various known results in categorical Galois theory and in particular two results of M. Barr and R. Diaconescu. We also give an elaborate list of examples and applications.

1 0

JOB OPENING: two post-doc positions rewriting and semantics
by KINOSHITA Yoshiki 01 Aug '97

01 Aug '97

The Semantics Group of the Computer Science Division of ETL seeks applicants for two postdoctoral positions in Rewriting and Programming Semantics which are expected to become available from October 15th, 1997. The positions are initially for one and half year (until March 31, 1999) with a possibility of extension to two and half year. The salary will be according to STA (Science and Technology Agency, which offers the budget for these positions) standards, depending on age and experience. The research interests of the group lies in Rewriting and Programming Semantics. Current topics are infinite rewriting and categorical semantics for data refinement. Applications, including a letter of interest, curriculum vita, e-mail address, and the names of at least three references, should be sent to our secretary: Ms Mariko Fujikubo, Computer Science Division, ETL, mailbox 1503 1-1-4 Umezono, Tsukuba, Ibaraki 305 JAPAN. To ensure full consideration, applications should be received by August 25, 1997, but we will accept applications until the positions are filled. Research facilities of the Semantics group are good: the research library and computer equipment are up-to-date. The semantics group currently enjoys support of a COE-grant (centre of excellence) by the Science and Technology Agency of Japan, which allows for invitation of visitors and research trips. The group has strong international connections and is active in organisation of and participation in in various regional and national workshops in Japan. Right now, there are three members: Dr. Yoshiki Kinoshita, Koichi Takahashi and Dr. Fer-Jan de Vries. The 106 year old Electrotechnical Laboratory (ETL) is a large governmental research institute. Research is performed in electronics and informatics; about one fourth of its 529 researchers do research in computer science, artificial intelligence and robotics. ETL is situated in Tsukuba Science City. Tsukuba is located about 50 km North-East of Tokyo with good connections to Tokyo and Narita international airport. For more details see (partly in Japanese) http://www.etl.go.jp/outline.html (on ETL) http://www.etl.go.jp/etl/etlclu/~semantics (on Semantics group) http://www.etl.go.jp/~yoshiki http://www.etl.go.jp/~ferjan Further enquiries can be made to Yoshiki Kinoshita (yoshiki(a)etl.go.jp) or Fer-Jan de Vries (ferjan(a)etl.go.jp) -- Yoshiki Kinoshita Computer Language Section, Electrotechnical Laboratory 1-1-4, Umezono, Tsukuba-shi, Ibaraki, 305 Japan phone: +81-298-54-5859 FAX: +81-298-50-3914 e-mail: yoshiki(a)etl.go.jp

1 0

My posting
by Michael Barr 01 Aug '97

01 Aug '97

I regret that my recent posting on Pratt's construction should not have been sent to categories. He sent me privately a construction showing that A -o A has at least 2^K dinatural endomorphisms (that is the diagonalization of the functor that takes A,B to A -o B) in chu(Set,K) and I mistakenly thought it had come off the categories bulletin board. But it had been sent to me privately. In any case, the claim is correct and my description for K = 2 is too. Sorry for the mixup. Michael

1 0