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Andrée Ehresmann (1935-2026)
by Isar Stubbe 24 Aug '26

24 Aug '26

Dear Colleagues, With great sadness, we inform you of the passing of Andrée Ehresmann (née Bastiani) on Friday, August 21, 2026, at her home in Amiens. Andrée Ehresmann played a major role in the category theory community for over sixty years. Born in Nice in 1935, she went as a young woman to Paris to study mathematics and Latin. She completed her doctoral thesis, and later her thèse d'État, in functional analysis, under the supervision of Gustave Choquet. From 1967, she was maître de conférences, and then professor, at the Université de Picardie in Amiens. It was Choquet who, already during her doctoral studies, encouraged her to take up category theory in the form that Charles Ehresmann was developing at that time. She later met Charles Ehresmann, who became her husband, and with whom she collaborated intensively until his death in 1979. Together they established the French school in category theory in Amiens, which became a vibrant research center, known internationally. From 1970 onwards, she was the driving force behind the Cahiers de Topologie et Géométrie Différentielle Catégoriques, which she directed until her passing. Andrée Ehresmann worked in various areas of category theory and pioneered the applications of categorical methods to the modeling of living and cognitive systems, mainly in collaboration with Jean-Paul Vanbremeersch. Her fundamental scientific contributions have been presented in an invited talk by René Guitart at the Séminaire Itinérant des Catégories held in Louvain-la-Neuve to celebrate her 90th birthday (https://www-lmpa.univ-littoral.fr/~sic/wordpress/?page_id=1609) The slides of René's talk are available here: https://www-lmpa.univ-littoral.fr/~sic/Louvain2025/Guitart.pdf On that occasion, she herself participated remotely and presented a talk, in French, about her scientific career: https://www-lmpa.univ-littoral.fr/~sic/Louvain2025/Ehresmann.pdf In the final months of her life, Andrée Ehresmann's health declined rapidly. Those who knew her personally appreciated her vision, leadership, generosity, and constant support of younger researchers. With her passing, the category theory community loses a prominent mathematician and a uniquely dedicated figure who contributed greatly to a historic era of French mathematics. Best regards, Isar Stubbe, Marino Gran, and René Guitart.

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Re: Andrée Ehresmann (1935-2026)
by Marco Grandis 23 Aug '26

23 Aug '26

Dear All, I wish to express my deep gratitude to Andrée. Her drive in unfolding categorical visions in new fields have played and are playing an important role in category theory. Her kindness and devotion have made her contribution unique. Regards Marco Grandis

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First Central European Category Theory Seminar
by bourkej 23 Aug '26

23 Aug '26

Dear all, We are pleased to announce that the first Central European Category Theory Seminar will take place at Masaryk University, Brno on Friday November 20th 2026. The idea of the meeting is to bring together researchers in category theory and related areas from around the local region in an informal setting to meet and discuss their research. We have invited speakers from Prague, Vienna and Budapest and will also welcome short contributions from attendees. Further information is available on the webpage. https://centraleuropeanctseminar.github.io/CECTSeminarBrno2026/ Anyone is welcome to attend but we ask you to register by September 30th so we have an idea of the numbers. This is essential if you would like to contribute a short talk or apply for some financial support to make the trip (we expect to have some money available for train/bus transport and hotel). If you have any questions, feel free to email any of the organisers. Look forward to seeing you there, The Organisers (John Bourke, Mike Lieberman, Lukas Vokřínek).

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Do localizations of categories always preserve initial objects and terminal objects? If so, is this recorded?
by Yemon Choi 21 Aug '26

21 Aug '26

Hello everyone, This is primarily a reference request, but I would also welcome corrections or indications of "better ways to approach this". I am not a category-theorist by training! My current PhD student and I have been looking at the localization of a certain subcategory of Grp, with respect to a class of morphisms that satisfy some but not all of the conditions for a left/right calculus of fractions. The key feature is that in the localization, every abelian group becomes isomorphic to the trivial group. We then wanted to show that every abelian group behaves as a zero object in the localized category (initial and terminal), and verified this in an ad hoc way. However, inspecting our arguments, they seem to work in much greater generality, leading to: CLAIM: let C be any category with a terminal object 1, and let W be any class of morphisms in C. Then 1 is a terminal object in the localization C[W^{-1}]. Initially this seemed too good to be true, since localization "adds more morphisms", but at the time of writing I can't find a mistake in our argument. Q1. Does anyone know a reference for this result/claim? The sources that I have consulted so far mostly discuss localization in contexts where C or W satisfy additional conditions, and say very little about general properties of the localisation functor when W is arbitrary. In the general setting I see no reason for the localisation functor to admit a left adjoint, which would be the cheapest way to show that it preserves terminal objects. Q2. Assuming we haven't made an error: is there a "conceptual" reason or explanation for this result? Our current argument relies on the concrete model of C[W^{-1}] in terms of equivalence classes of zigzags (a la Gabriel-Zisman), and shows that any zigzag starting at an object A_0 and ending at 1 is equivalent to the unique C-morphism A_0 \to 1. The proof is "hacky": it works by performing an induction on the length of the zigzag, and requires a small but mildly annoying case-by-case analysis. I have often been told that a "true" categorical perspective should just use the appropriate universal property of localization (perhaps in a 2-categorical context), but at the moment I can't see a way to achieve this. Remark: essentially the same reasoning seems to show that localization preserves initial objects, so both Q1 and Q2 apply to that result/claim. Regards Yemon -- Dr. Y. Choi School of Mathematical Sciences Lancaster University Bailrigg, Lancaster Lancashire LA1 4YF

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RHPL@FSTTCS 2026: Call for Proposals
by Abhisekh Sankaran 21 Aug '26

21 Aug '26

TCS Confidential ============================================================= CALL FOR PROPOSALS RHPL@FSTTCS 2026: Workshop on Research Highlights in Programming Languages + Dates: December 16 - 18, 2026 + Venue: IIT Delhi, co-located with FSTTCS 2026 + Website: https://fmindia.cmi.ac.in/rhpl2026/ + Submission deadline: September 28, 2026 IST ============================================================= Dear Colleague, As you may know, FSTTCS 2026 (https://www.fsttcs.org.in/2026/) will be held at IIT Delhi (https://home.iitd.ac.in/) during December 16 - 18, 2026. The conference is organized by IARCS, the Indian Association for Research in Computing Science (https://www.iarcs.org.in/) in association with ACM India (https://india.acm.org/) It is a very visible forum for presenting original results in foundational aspects of Computer Science and Software Technology. As in previous years, the Workshop on Research Highlights in Programming Languages (RHPL) will be co-located with the main FSTTCS conference. The workshop is organized jointly by IARCS and iPLAN (the India Chapter of ACM SIGPLAN; https://india.acm.org/chapters) The focus of the workshop will be on all areas of Programming Languages. The objective of RHPL is to foster interactions between the attendees of the workshop, and more broadly researchers working on Programming Languages, and the traditional FSTTCS community of researchers working on Theoretical Computer Science and Formal Methods. We invite proposals for: + Talks: based on recent work that has been published in reputed venues, or is mature in terms of approach and evaluation. + Posters: - Regular: Based on early ideas that are promising but have not been developed fully. Selections of these proposals will be made based on the promise of research possibilities and their novelty. - Student: Based on unpublished work at any stage. Selected proposals will be included in a student poster competition that will be judged by a panel of experts. More details on the submission topics, submission guidelines and the student poster competition can be found below. --------------- Websites: --------------- RHPL 2026: https://fmindia.cmi.ac.in/rhpl2026/ RHPL 2025: https://fmindia.cmi.ac.in/rhpl2025/ ============= Important Dates ============= All dates below are in Indian Standard Time (IST). - Submission portal opens: August 21, 2026 - Submission deadline: September 28, 2026 - Notification: October 7, 2026 - Early registration deadline: TBA - RHPL@FSTTCS: December 16 - 18, 2026 =============== Submission Topics =============== The submission topics include, but are not limited to, the following: - Applied formal methods - Automated and interactive theorem provers - Compilers - Concurrency and memory models - Domain and type theories - Program analysis and verification - Program sketching, synthesis, and repair - Programming language design and semantics Further, in view of the increasing role of Artificial Intelligence (AI) and Machine Learning (ML) in PL theory and practice, the workshop explicitly includes in its scope themes at this intersection. Of particular interest are the roles of Large Language Models (LLMs) in PL, such as in design and code synthesis, as well as broader mutual influences between AI/ML and PL; for instance, probabilistic programming languages. ==================== Student Poster Competition ==================== We invite students at all stages, from undergraduate to PhD, to submit poster proposals based on their unpublished work. For graduate students, only individual work is allowed to be presented. If the work is being done as part of a group, then the presenters must focus on their individual contributions. Undergraduates can present their individual work and also work done in (undergraduate) team projects. The evaluation of the posters will be on the basis of the technical strength of the work, the presenter's awareness of related literature, and the quality of the poster and presentation. The results will be announced on the RHPL 2026 website following the competition. ================ Submission Guidelines ================ Proposals to the workshop may be submitted using the form below. https://forms.fillout.com/t/7ePHh773f2us Proposals for talks may be based on published or unpublished work. Proposals for posters are only for unpublished work. For both formats, submissions may present either a single study, such as in an individual paper or an unpublished manuscript, or a body of research. Multiple proposal submissions are allowed. Each proposal must be submitted as a single PDF file. Any reasonable style file can be chosen. The proposal page limits are as below; the page counts exclude references. Appendices are to be avoided, and references may contain pointers to papers, preprints, technical reports, or manuscripts under progress that the proposal is based on. + Talks: - Proposals based on work that is published: 2 pages - Proposals based solely on unpublished work: 4 pages + Posters: - Regular (non-student) proposals: 2 pages - Student proposals: 4 pages Talk proposals based on unpublished work and student poster proposals will be provided short referee reports along with their decision notifications. There are no publications of the workshop. Accepted proposals may be compiled into a booklet of abstracts/proposals to be made available on the RHPL 2026 website. ======= Contact ======= For any queries, feel free to write to us at the addresses below. - pankaj.kumar.kalita(a)ibm.com<mailto:pankaj.kumar.kalita@ibm.com> - abhisekh.sankaran(a)tcs.com<mailto:abhisekh.sankaran@tcs.com> We look forward to receiving your talk/poster proposals to the workshop. On behalf of the RHPL@FSTTCS workshop organizing committee: Pankaj Kumar Kalita (IBM Research) (co-Chair) Abhisekh Sankaran (TCS Research) (co-Chair) Deepak D'Souza (IISc Bangalore) Uday Khedker (IIT Bombay) Kumar Madhukar (IIT Delhi) Kartik Nagar (IIT Madras) Ganesan Ramalingam (Microsoft) Abhik Roychoudhury (National University of Singapore) Divyesh Unadkat (Synopsys) =====-----=====-----===== Notice: The information contained in this e-mail message and/or attachments to it may contain confidential or privileged information. If you are not the intended recipient, any dissemination, use, review, distribution, printing or copying of the information contained in this e-mail message and/or attachments to it are strictly prohibited. If you have received this communication in error, please notify us by reply e-mail or telephone and immediately and permanently delete the message and any attachments. Thank you

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Pacific Category Theory Seminar (Online) - Friday, August 28
by JS Lemay 21 Aug '26

21 Aug '26

Dear all, Alyssa Renata (Imperial College London) will give a talk for a second edition of this month's PCT seminar (https://pctseminar.github.io/) on Friday August 28 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: The Game Spectrum of a Monad? Abstract: In recent work joint with Richard Garner and my supervisor Nicolas Wu, inspired by the computational effects interpretation of monads and algebraic theories due to Moggi, Plotkin and Power, we constructed an adjunction between the category of monads on set and the category of small categories and retrofunctors/cofunctors. Under the computational effects interpretation, the monad encodes computations which may interact with or affect some environment. The left adjoint to this construction assigns to each monad what is called its **behaviour category**, which may be seen as a model of the environment itself: the objects are the possible states, and the morphisms transitions between states. This adjunction ought to be seen as a kind of duality, with the behaviour category acting as the spectrum of a monad. The first half of the talk will be dedicated to reviewing this construction and its surrounding adjunction. The second half of the talk is about my recent attempt with Richard at rectifying a defect of the theory: many monads have trivial behaviour category! This is undesirable because of an analogy we want to develop with schemes: the monads replace the (commutative) rings, while the behaviour category should replace the affine schemes. But of course, an affine scheme/spectrum should faithfully encode its corresponding ring/monad, and this is evidently not so for the behaviour category. Our proposal then is to replace the behaviour category by a particular 2-player game (between the program and the environment), from which the data of the behaviour category can be extracted by inspecting its (winning) strategies. The point is that the behaviour category is trivial when there are no winning strategies, but this need not imply triviality of the game itself. To be more precise, we will investigate the relationship with the template games of Paul-Andre Mellies, which he used to build higher-dimensional models of linear logic. We hope to see you there! Talks after posted on youtube afterwards: https://www.youtube.com/@PCTSeminar Best wishes, Soichiro Fujii, Zeinab Galal, JS PL

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PhD and Postdoc in the theory of comonads
by Tomáš Jakl 19 Aug '26

19 Aug '26

Dear All, I'm looking for a postdoc and PhD student to work with me on the study of both the theory and applications of comonads. We aim to build the theory of presentations of comonads to be able to specify computational resources in a principal way. Therefore, the project is in the intersections of category theory, linear type theory, programming language semantics and potentially also finite model theory (via game comonads), theory of concurrency and so on. For details, see https://tomas.jakl.one/projects/unicator Feel free to pass my announcement to potential candidates, should you know any. Thank you, Tomas

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ESSLLI 2027: Call for course and workshop proposals
by Danel Ahman 19 Aug '26

19 Aug '26

(For 2027, it would be great to have more courses at the intersection of the traditional ESSLLI topics (logic, language, information) and category theory.) --- ESSLLI 2027: European Summer School in Logic, Language and Information 2027 University of Tartu Tartu, Estonia, August 2-13, 2027 Conference web page: https://digits.ut.ee/esslli-2027/ Submission link: https://easychair.org/conferences/?conf=esslli2027 **TL;DR:** ESSLLI seeks courses on diverse topics, each course taking one or two weeks of 90 minutes per day. ESSLLI workshops follow the same structure (5 days, 90 minutes per day) with content assembled from external contributors. # Important Dates October 1, 2026 (AoE): Deadline for submitting course/workshop titles October 15, 2026 (AoE): Deadline for submitting course/workshop proposals December 10, 2026 (AoE): Notification sent to course/workshop proposers Note that submitting a proposal requires that the person submitting has an Easychair profile. # Introduction Under the auspices of the Association for Logic, Language, and Information (FoLLI), the European Summer School in Logic, Language, and Information (ESSLLI) runs every year. Except for 2021, when the school was virtual, it runs in a different European country each year. It takes place over two weeks in the summer, hosts approximately 50 different courses at levels that run from foundational to introductory to advanced, and attracts around 400 participants from all over the world. In 2027, ESSLLI will visit Tartu and Estonia for the first time in its history. Since 1989, ESSLLI has been providing outstanding interdisciplinary educational opportunities in the fields of Computer Science, Cognitive Science, Linguistics, Logic, Philosophy, and beyond. It comes from a community which recognizes that advances in our common areas require the contributions of multiple interrelated disciplines. The main focus of ESSLLI is the interface between linguistics, logic and computation, with special emphasis on human linguistic and cognitive ability. Courses, both introductory and advanced, cover a wide variety of topics within the combined areas of interest: Logic and Computation, Computation and Language, and Language and Logic. Workshops are also organized, providing opportunities for in-depth discussion of issues at the forefront of research, as well as a series of invited evening lectures. # Topics and Format Proposals for courses and workshops at ESSLLI 2027 are invited in all areas of Logic, Linguistics and Computer Science. Cross-disciplinary and innovative topics are particularly encouraged. Each course and workshop will consist of five 90 minute sessions, offered daily (Monday-Friday) in a single week. Proposals for two-week courses should be structured and submitted as two independent one-week courses, e.g. as an introductory course followed by an advanced one. In such cases, the ESSLLI Program Committee reserves the right to accept just one of the two proposals. All instructional and organizational work at ESSLLI is performed completely on a voluntary basis, so as to keep participation fees to a minimum. However, organizers and instructors have their registration fees waived, and are reimbursed for travel and accommodation expenses up to a level to be determined and communicated with the proposal notification. ESSLLI can only guarantee reimbursement for at most one course/workshop organizer, and cannot guarantee full reimbursement of travel costs for lecturers or organizers from outside of Europe. The ESSLLI organizers would appreciate any help in controlling the School's expenses by seeking partial or complete coverage of travel and accommodation expenses from other sources. Courses can have any number of instructors, but any instructors listed are expected to attend. # Categories Each proposal should fall under one of the following categories. ## Foundational Courses Such courses are designed to present the basics of a research area, to people with no prior knowledge in that area. They should be of elementary level, without prerequisites in the course's topic, though possibly assuming a level of general scientific maturity in the relevant discipline. They should enable researchers from related disciplines to develop a level of comfort with the fundamental concepts and techniques of the course's topic, thereby contributing to the interdisciplinary nature of our research community. ## Introductory Courses Introductory courses are central to ESSLLI's mission. They are more sophisticated than Foundational courses but less specialized than Advanced courses. They are intended to introduce a research field to students, young researchers, and other non-specialists, and to foster a sound understanding of its basic methods and techniques, but will assume a greater level of maturity in students compared to foundational courses. Such courses should enable researchers from related disciplines to develop some comfort and competence in the topic considered. Introductory courses in a cross-disciplinary area may presuppose general knowledge of the related disciplines. ## Advanced Courses Advanced courses are targeted primarily to graduate students who wish to acquire a level of comfort and understanding in the current research of a field. ## Workshops Workshops focus on specialized topics, usually of current interest. Workshop organizers are responsible for soliciting papers and selecting the workshop program. They are also responsible for publishing proceedings if they decide to have proceedings. # Proposal Guidelines Course and workshop proposals should closely follow these guidelines to ensure full consideration. Course and Workshop proposals can be submitted by no more than two lecturers/organizers and can be presented by no more than these two lecturers/organizers. Two is actually the preferred number of lecturers/organizers, to secure the course/workshop against unexpected unavailability. All instructors and organizers must possess a PhD or equivalent degree by the submission deadline. Course proposals should mention explicitly the intended course category. Proposals for introductory courses should indicate the intended level, for example as it relates to standard textbooks and monographs in the area. Proposals for advanced courses should specify the prerequisites in detail. Proposals of Courses given at ESSLLI in the previous year will have a lower priority of being accepted in the current year. Proposals must be in PDF format and include all the following information: 1. Personal information for each proposer: Name, affiliation, contact address, email, homepage (optional) 2. General proposal information: Title, category 3. Contents information: * Abstract of up to 150 words * Motivation and description (up to two pages) * Tentative outline * Expected level and prerequisites * Appropriate references (e.g. textbooks, monographs, proceedings, surveys) 4. Information required of course proposers: * Will the course appeal to students outside of the main discipline of the course? * What experience does the proposer have in presenting an intensive one-week interdisciplinary setting? * What evidence is there that the course proposer is an excellent lecturer? 5. Information required of workshop organizers: * Information on relevant preceding meetings and events, if applicable. * Information about potential external funding for participants. A typical proposal fits 3 pages. # Submission Information By October 1, 2026 (AoE), proposers are asked to submit at least the name(s) of the instructor(s), the ESSLLI area+course level and a title and short abstract for the proposed course/workshop. By October 15, 2026 (AoE), course proposers must complete their submission by uploading a PDF with the actual proposal as detailed above. # Submission Portal Please submit your proposals to easychair. # EACSL Sponsorship The EACSL will support one Logic and Computation course or workshop addressing topics of interest to Computer Science Logic (CSL) conferences. The selected course or workshop will be designated an EACSL course/workshop in the programme. If you wish to be considered for this, please indicate it in your proposal. # Program committee Chair * Michael Benedikt, Oxford University, UK Local co-chair * Danel Ahman, University of Tartu, Estonia Language and Logic * Fausto Carcassi, University of Amsterdam, the Netherlands * Peter Sutton, Potsdam University, Germany * Wateru Uegaki, University of Edinburgh, UK Language and Computation * Jon Rawski, San Jose State University, USA * Kyle Richardson, Allen Institute for Artificial Intelligence, USA * Shane Steinert-Threlkeld, University of Washington, USA Logic and Computation * Dana Fisman, Ben-Gurion University, Israel * Michael Hahn, Saarland University, Germany * Thomas Zeume, Ruhr University Bochum, Germany

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Algebra Down Under 2026, the 10th Australian Algebra Conference (16-20 Nov 2026)
by JS Lemay 10 Aug '26

10 Aug '26

[[Send on behalf of the organisers]] Dear colleagues, We are pleased to announce Algebra Down Under 2026, the 10th Australian Algebra Conference, which will be held at Western Sydney University in Sydney, Australia, from 16–20 November 2026. The conference will bring together mathematicians working across a broad range of areas in algebra, including category theory, representation theory, K-theory, universal algebra, operator algebras, noncommutative algebra, group theory, algebraic geometry, semigroup theory, graph theory, and coding theory. Registration is now open through the conference website: https://adu2027.github.io/10thaac/ Early-bird registration closes on 30 September 2026. The early-bird fees are AUD 180 for academics and general participants, and AUD 100 for students, postdoctoral researchers, and early-career researchers. The submission link for contributed talks will be available shortly on the conference website. Talk submissions and conference registration will be handled separately, so those interested in presenting a talk are welcome to register now. Further information, including the list of invited speakers, is available on the conference website. Questions may be directed to adu(a)westernsydney.edu.au<mailto:adu@westernsydney.edu.au>. We would be grateful if you could share this announcement with interested colleagues and students. Best wishes, The Algebra Down Under 2026 Organising Committee

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[CFP] Relational and Algebraic Methods in CS — Thematic Issue of Fundamenta Informaticae
by Luigi Santocanale 09 Aug '26

09 Aug '26

(Apologies for multiple posting) OPEN CALL FOR PAPERS FOR JOURNAL THEMATIC ISSUE Relational and Algebraic Methods in Computer Science Thematic Issue of the journal Fundamenta Informaticae (FI) https://fi.episciences.org/ IMPORTANT DATES: Submission Deadline: 31/10/2026. Notification (tentative): 30/04/2027. TOPICS: Relational and algebraic methods belong to the core of computer science. This special issue aims to showcase the variety and relevance of recent developments in this field ranging from theory to applications. We invite submissions of high-quality original research articles in the general fields of algebras relevant to computer science and applications of such algebras. Topics include but are not limited to: * Theory - algebras such as semigroups, residuated lattices, semirings, Kleene algebras, relation algebras and quantales - their connections with program logics and other logics - their formalisation with theorem provers - their use in the theories of automata, concurrency, formal languages, games, networks and programming languages - the development of algebraic, algorithmic, category-theoretic, coalgebraic and proof-theoretic methods for these theories * Applications - tools and techniques for program correctness, specification and verification - quantitative and qualitative models and semantics of computing systems and processes - algorithm design, automated reasoning, network protocol analysis, social choice, optimisation and control - industrial applications While we welcome substantially extended versions of papers published in the proceedings of the RAMiCS 2026 conference (Springer LNCS 16526, https://link.springer.com/book/10.1007/978-3-032-22469-9) this call is open to anyone interested in the field of relational and algebraic methods. SUBMISSION INSTRUCTIONS: All submissions will be evaluated solely with respect to their novelty, significance and technical quality according to the high standards of the journal FI. They must adhere to the standard FI guide for authors: https://fi.episciences.org/page/author-guidelines Authors must first prepare a preprint and post it on CoRR/arXiv or HAL (https://hal.science/) An account on one of these platforms is required prior to submission. Authors should then upload their manuscript to the Episcience online system as follows: - [Create and] sign in to your episciences account (https://fi.episciences.org/user/) - Go to https://fi.episciences.org/submit/index. - Insert your manuscript arXiv or HAL identifier and click "Search". - On the next page, pick "Relational and Algebraic Methods in Computer Science" from the menu list "Submit in the volume:". - Complete the rest of the form in the page and submit. Deviation from these requirements may lead to immediate rejection. EDITORS: Uli Fahrenberg (LMF, Paris-Saclay University, France, guest editor FI) Wesley Fussner (Institute of Computer Science, Czech Academy of Sciences, Prague, Czechia, guest editor FI) Luigi Santocanale (LIS, Aix-Marseille Université, France, guest editor FI) -- Luigi Santocanale, professeur, LIS/AMU

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