July 2026 - Categories - categories.org.au

Plotkin80 / LFCS40 / Wadler70
by Ohad Kammar 31 Jul '26

31 Jul '26

Hi everyone, I apologise for cross-posting this, I'm making sure this reaches everyone who may be interested in case people dropped off mailing lists etc over the past 40 years. Please forward to other networks if relevant. In brief: pre-registration for these events closes **today** and does not require payment, you only need to pay later. Yours, Ohad. # Plotkin 80 / LFCS 40 / Wadler 70 September 7-9, 2026 Edinburgh, Scotland ** Pre-registration for this event is now open (_ends today_): ** https://forms.cloud.microsoft/e/dBqqyYBJ39 Please pre-register by July 31. The proper registration and payment system will be available from August 7. Founded in 1986 by Rod Burstall, Robin Milner, Gordon Plotkin and Matthew Hennessy, the Laboratory for Foundations of Computer Science is a community of theoretical computer scientists with interests in research topics such as concurrency, semantics, categories, algebra, types, logic, algorithms, complexity, databases, security and cryptography, and quantum computing, and their applications in Computer Science and beyond. LFCS40 is a celebration of forty years of innovation in these areas. http://events.inf.ed.ac.uk/lfcs40 LFCS40 will take place in Edinburgh on September 8th, 2026 with a programme of talks from current and former members of the LFCS, visitors, and friends. Two related events celebrating significant birthdays of Gordon Plotkin (co-founder and former Director) and Philip Wadler (Emeritus Chair of Theoretical Computer Science and former Director) are also taking place immediately before after LFCS40. Registration covers all three events. Confirmed invited speakers include: ## (September 7) Plotkin 80: A symposium in honour of Gordon Plotkin's 80th birthday http://events.inf.ed.ac.uk/plotkin80 Samson Abramsky (University College London, University of Oxford) Danel Ahman (University of Tartu) Marcelo Fiore (University of Cambridge) Philippa Gardner (Imperial College London) Dominic Hughes (U.C. Berkeley) David Pym (UCL & Institute of Philosophy, University of London) Rob van Glabbeek (University of Edinburgh) Glynn Winskel (Queen Mary London, University of Cambridge) Ningning Xie (University of Toronto, Google DeepMind) ## (September 8) LFCS 40: A symposium celebrating the 40th anniversary of the founding of the Laboratory for Foundations of Computer Science https://events.inf.ed.ac.uk/lfcs40/ Tariq Elahi (University of Edinburgh) Sybille FrÃ¶schle (TUHH - Hamburg University of Technology) Andrew D. Gordon (Cogna/ARIA) Martin Grohe (RWTH Aachen) Heng Guo (University of Edinburgh) Chris Heunen (University of Edinburgh) Leonid Libkin (University of Edinburgh) Prakash Panangaden (McGill University) Elizabeth Polgreen (University of Edinburgh) Moshe Vardi (Rice University) ## (September 9) Wadler 70: A symposium in honour of Phil Wadler's 70th birthday http://events.inf.ed.ac.uk/wadler70 John Hughes (Chalmers) Conor McBride (Strathclyde) Orestis Melkonian (Kodamai) Liam O'Connor (ANU) Jeremy Siek (Indiana) Peter Thiemann (Freiburg) Nobuko Yoshida (Oxford) The University of Edinburgh is a charitable body, registered in Scotland, with registration number SC005336. Is e buidheann carthannais a th' ann an Oilthigh Dhùn Èideann, clàraichte an Alba, àireamh clàraidh SC005336.

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Pacific Category Theory Seminar (Online) - Friday, August 7
by JS Lemay 30 Jul '26

30 Jul '26

Dear all, Sveta Makarova (ANU) will give a talk for this month's PCT seminar (https://pctseminar.github.io/<https://pctseminar.github.io>) on Friday August 7 at 10am JST/11am AED (1am UTC). The zoom link to join the seminar is: https://kyoto-u-edu.zoom.us/j/82401794000?pwd=VjVmzVjmlgxhkdHES4xYeQBTpMzQk… Title: Contractions and flops via moduli of non-pure sheaves Abstract: The goal of the talk is to convince the audience that 2-categorical enhancements of some classical geometric objects yield interesting geometric constructions. Consider the stack of ideal sheaves of l points on a smooth projective variety X. Its good moduli space is the well-known Hilbert scheme of l points Hilb^l(X). In this talk, I will define a certain enlargement U of this stack and prove that it admits a good moduli space. Furthermore, I will describe a different open substack of U that admits a good moduli space and explain how it yields a surgery diagram via non-GIT wall-crossing. As an application in the toy case l=1, I will explain how this construction helps contract rational curves on higher-dimensional varieties and, time permitting, use the interpretation of the surgery as a fine moduli of sheaves to prove instances Kawamata’s DK-hypothesis in this setting. This is joint work with Andres Fernandez Herrero. We hope to see you there! If you cannot make it, talks after posted on youtube afterwards: https://www.youtube.com/@PCTSeminar Best wishes, Soichiro Fujii, Zeinab Galal, JS Lemay

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Eduardo Dubuc
by Joyal, André 30 Jul '26

30 Jul '26

Dear category theorists, Sad news. My friend Eduardo Dubuc passed away Monday (July 27, 2026) after having a stroke. while teaching math at the University of Buenos-Aires. He was almost 84. He was visiting professor at UQAM until 1980, and professor at the UBA until his death. Eduardo received his Phd in 1969 from the University of Chicago under the supervision of Saunders MacLane with a thesis on Kan extension in enriched categories. His SLN monograph on the subject was the first systematic theory of enriched colimits and of enriched Kan extensions. Eduardo worked on a large variety of subjects throughout his life. https://scholar.google.com/citations?user=3fiEMcgAAAAJ&hl=en To illustrate the diversity of his work I will give a few examples. He introduced the Elevator Calculus for 2-categories around 1970, a precursor of Penrose diagrams and of string diagrams developed 15 years later by Ross Street and myself for applications to monoidal categories. He introduced and developed a theory of Tannaka duality for localic groups in a topos, with applications to the Grothendieck Galois theory developed by Myles Tierney and myself. He developed a theory of quasi-topoi with Jacques Penon, later included in the Sketches of an Elephant by P.T. Johnstone. He constructed the first full model of synthetic differential geometry in collaboration with Marta Bunge and Jacques Penon, it became the backbone of the book by Gonzalo Reyes and Ieke Moerdijk. He extended Stone duality to MV-algebras in collaboration with Roberto Cignoli et Daniele Mundici. He introduced a notion of Quillen model 2-category and a theory of 2-localizations with M.E. Descotte and Martin Szyld. He gave a construction of the 2-filtered bicolimits of bicategories in collaboration with Ross Street. His work has applications in every corner of category theory. Eduardo was a problem solver with the skills of a theory builder. He was a pleasant person to work with, eager to explore new territories. He was also a great math teacher. See you later Eduardo, André

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Reference for the analytic vs. synthetic distinction in mathematics
by José Manuel Rodríguez Caballero 27 Jul '26

27 Jul '26

Dear all, I would like to include the following distinction in a manuscript: There are two styles of reasoning in mathematics: 1. *analytic*: structures built from a “point-set” substrate; 2. *synthetic*: axioms imposed directly on the available types. At present, the only source I have found stating this distinction in this form is the nLab page on synthetic mathematics ( https://ncatlab.org/nlab/show/synthetic+mathematics ). Could anyone point me to a published reference where this terminology or this formulation of the analytic vs. synthetic approaches is explicitly discussed? Many thanks in advance. Best regards, JMRC

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PSSL 113: Final Call for Abstracts
by Marco Abbadini 21 Jul '26

21 Jul '26

Dear Colleagues, This is a final reminder that the deadline for abstract submission for the *113th Peripatetic Seminar on Sheaves and Logic (PSSL 113)* is *31 July 2026*. The conference will take place at the Université catholique de Louvain, in Louvain-la-Neuve, Belgium, on *26–27 September 2026*. Conference website: https://sites.uclouvain.be/pssl113 Contributed talks on all aspects of category theory and its applications are welcome. Abstracts should be at most one page, including references, and should be submitted using the template available on the conference website. *Important dates:* - *31 July 2026:* Abstract submission deadline. - *15 August 2026:* Registration deadline. - *26–27 September 2026:* PSSL 113. Attendance is free, but registration is required. For enquiries, please contact *pssl.113.uclouvain(a)gmail.com*. We look forward to receiving your submission and to welcoming you in Louvain-la-Neuve. Best regards, Marco Abbadini, Marino Gran, Tim Van der Linden and Enrico Vitale

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Dedicated to R. H. Street’s 80
by Steve Lack 20 Jul '26

20 Jul '26

Dear Colleagues, The submission deadline for the special issue of JPAA in honour of Ross Street has been extended to October 31, 2026. Also sending us an "Intention to submit" message by the end of September would be helpful. Best regards, J. Adamek, M.M. Clementino, M. Gran, G. Janelidze, S. Lack

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Did you see this characterisation of Z in the 70s?
by David Roberts 08 Jul '26

08 Jul '26

Hi all, I'm requiring the brains trust of the older generation to let me know if the following definition (as exactly like this as possible) was in the air or written down pre-1980. I will assume C is a cartesian closed category, but perhaps it was stated for C a topos at the time. Definition: Let C be a cartesian closed category. An _integers object_ is a pointed object 0 : 1 --> Z with the data s : Z ---> Z and p : Z ---> Z such that p = s^{-1}, and is the initial among pointed objects with an automorphism. I have found this definition published in a computer science paper: * Turner, D.A. (1985). Miranda: A non-strict functional language with polymorphic types. In: Jouannaud, JP. (eds) Functional Programming Languages and Computer Architecture. FPCA 1985. Lecture Notes in Computer Science, vol 201. Springer, Berlin, Heidelberg. https://doi.org/10.1007/3-540-15975-4_26 and something very similar in papers in 1982 and 1980 coming from the ADJ school of computer science (heavily influenced by category theory). There it's stated more in terms of giving the definition of a algebraic data type in some inductive means. But I can't find it in the category theory literature proper. I don't know if it came from some old logic/set theory paper, or was from CT, or was just first written down by computer scientists, but it was so incredibly obvious no one wrote it down in mathematics. Please note that "well the definition is obvious" _now_ is not really sufficient, I'd like to hear from someone from pre-1980 who can say "I recall discussing this definition at the time and it was so obvious then that no one wrote it down" if this is the type of answer I'm going to get. Moreover, since I'm interested in the case where I can't assume I have colimits, any early mention _constructing_ an object of integers from the NNO in a topos in "the usual way" also isn't useful (what colimits does a CCC have for free? Certainly not quotients or pushouts) More recently (in the last decade) this characteristion has been used in MLTT/Homotopy Type Theory, and this being written on the nLab in a purely categorical way is what alerted me to the characterisation. I'm hoping to get a reference to add there, aside from the computer science ones which strike me as very likely influenced by something a category theorist could have written down. Thanks in advance, David -- Dr David Roberts http://ncatlab.org/nlab/show/David+Roberts Adjunct Associate Lecturer School of Mathematical Sciences Adelaide University — Tirkangkaku SA 5005 AUSTRALIA Australian University Provider Number PRV14404 CRICOS Provider Number 04249J ----------------------------------------------------- IMPORTANT: This email may be privileged and/or confidential, and the sender does not waive any related rights and obligations. Any distribution, use or copying of this email or the information it contains by other than an intended recipient is unauthorised. If you receive this email in error, please advise me (by return email or otherwise) immediately.

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First announcement of "Types and Structure 2027" (TS2027) - in memory of Thomas Streicher
by Benno van den Berg 08 Jul '26

08 Jul '26

[APOLOGIES FOR MULTIPLE POSTINGS] Dear all, This is the first announcement for a workshop on "Types and Structures" (TS2027) that will be held in Padova in the week of 24–28 May in 2027. The workshop will be dedicated to the scientific legacy of our friend and colleague Thomas Streicher. The website of the event can be found here: https://ulrikbuchholtz.dk/ts2027/ Please mark it in your calendars! We also encourage you to book your accommodation at your earliest convenience, as Padova is a popular destination during May. To contact us, please use the email address: typesandstructures2027(a)gmail.com We hope to see many of you at the event! Best wishes, Benno van den Berg Ulrik Buchholtz Jonas Frey Milly Maietti Jonathan Weinberger

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Pacific Category Theory Seminar (Online) - Friday, July 7
by Zeinab Galal 06 Jul '26

06 Jul '26

Dear all, Lili Shen (Sichuan University) will give a talk for this month's PCT seminar (https://pctseminar.github.io/) on Friday, July 10th at 10am JST/11am AED (1am UTC). The zoom link to join the seminar is: https://kyoto-u-edu.zoom.us/j/82401794000?pwd=VjVmzVjmlgxhkdHES4xYeQBTpMzQk… Title: Towards the categorical foundation of quantale-valued sets Abstract: A classical set may be regarded as a set equipped with an equality relation valued in the two-element Boolean algebra. Fourman and Scott generalized this idea by introducing Î©-sets, where equality is valued in a frame Î©; this construction is closely related to sheaves and topos theory. HÃ¶hle and his collaborators later developed the theory of quantale-valued sets, replacing the frame Î© by a quantale Q. This talk provides an overview of the theory of quantale-valued sets and the ongoing efforts to establish its categorical foundation. I will explain why Q-sets form a natural and interesting generalization of FourmanâScott Î©-sets, and then present two recent results that clarify the extent to which the category of Q-sets behaves like the category of sets or the category of Î©-sets. First, for a commutative and divisible quantale Q, the category of Q-sets is a topos if and only if Q is a frame. Second, for the unit interval [0,1] equipped with a continuous t-norm *, the category of ([0,1], *)-sets is cartesian closed if and only if * is the minimum t-norm. We hope to see you there! Best wishes, Soichiro Fujii, Zeinab Galal, JS Lemay

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