- Categories - Listes du LIPN

Fwd: Seminar "axe complexités": Damiano Mazza on 22/05 (joint with gdt Catégories)
by Groupe de travail catégories 18 May '26

18 May '26

Hi all! There are a lot of holidays in May, so we haven't seen each other in a while. This Friday, Damiano will be presenting a joint talk between our GdT and the complexités GdT. Abstract below. See you there! Morgan -------- Courriel original -------- Objet: Seminar "axe complexités": Damiano Mazza on 22/05 (joint with gdt Catégories) Date: 2026-05-18 14:19 De: Sylvain Perifel <perifel(a)lipn.univ-paris13.fr> À: "lipn.tous(a)lipn.univ-paris13.fr" <lipn.tous(a)lipn.univ-paris13.fr> Cc: hoffbeck(a)math.univ-paris13.fr Dear all, The next "Axe complexités seminar" is joint with the "Groupe de travail Catégories" and will take place next Friday at 10:30. Note the *unusual date and time*. When: Friday, May 22, at 10:30 Where: room B107 Speaker: Damiano Mazza (LIPN) Title: Constraint satisfaction problems: between complexity and categorical algebra (see abstract below) As usual, the talk is intended for a wide audience. In case you want to attend online, the BBB room will be at https://bbb.lipn.univ-paris13.fr/b/mus-djh-bjk-ljz For past talk videos, as well as future planned talks, please see the website: https://lipn.univ-paris13.fr/~mustafa/AxeComplexites/ See you on Friday! Nabil & Sylvain ---------- Speaker: Damiano Mazza Title: Constraint satisfaction problems: between complexity and categorical algebra Abstract: Constraint satisfaction problems (CSP) are a vast class of problems naturally arising in practical context, especially combinatorial optimization. In the early 90s, Feder and Vardi conjectured that CSPs enjoy a dichotomy: a CSP either admits a polynomial-time algorithm or can be proved to be NP-complete. Building on the work of several people spanning about 25 years, Bulatov and Zhuk indpendently proved the conjecture in 2017, and Feder and Vardi were awarded the Church Prize for starting this research area. The theory of CSPs heavily relies on tools from universal algebra. Very recently, Hadek, Jakl and Opršal found a categorical reformulation which neatly reorganizes and generalizes this theory. I will present my understanding of Hadek, Jakl and Opršal's paper (which has been accepted at LICS 2026) and I will introduce CSPs and their theory trying to keep as much as possible the parallel between the usual, combinatorial definitions and the categorical ones, and hopefully manage to give an idea of the proof of the hardness part of the dichotomy theorem, i.e., that "hard" CSPs are necessarily NP-complete.

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GdT informel ce matin
by Groupe de travail catégories 17 Apr '26

17 Apr '26

Hi! Some regular attendees of the working group are away in Venice, but for anyone that would like to meet up in B107 anyway, I'd like to discuss categories with you! In particular: - Jad is back from Japan, where there was a workshop on Differential Categories - I have an idea I'm developing called *interactegories* which I would like to talk about. Maybe see you there at 10:30. I'll open the BBB too. If no one shows, I'll end the meeting early :) Morgan

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Pas de GdT demain
by Groupe de travail catégories 09 Apr '26

09 Apr '26

Hi, We have no working group planned for tomorrow. We'll meet one more time next week before the university closes for the holidays. Best, Morgan

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These MathStic
by Groupe de travail catégories 08 Apr '26

08 Apr '26

Bonjour, il y aura une boruse mathSTIC cette année, dont la règle est qu'il faut un co-encadrement sur 2 laboratoires. J'ai un élève de M2 très bon qui cherche une possible thèse à paris. Il s'agit de Grzegorz Czech (un nom prédestiné). Je ne sais pas si il y a des gens qui ont des idées de sujet qui marcheraient dans ce cadre : Quelques infos que je copy paste : "Recently my studies have been focused on homotopy theory and its structural foundations, with particular attention to higher categorical and higher algebraic structures. I am drawn to questions where homotopy-theoretic methods make contact with geometry, algebra, or mathematical physics. My master's thesis, currently in progress under the supervision of Karol Szumiło at the University of Warsaw, develops a theory of a particular class of Grothendieck fibrations over 2-groupoids, which we call 2-coverings. The project is motivated by the observation that classical covering space theory admits a reformulation in terms of functors from the fundamental groupoid into sets, which extends elegantly to ∞-groupoids via Lurie's straightening-unstraightening. The intermediate case of 2-groupoids — which the modern literature tends to bypass — turns out to be tractable and concretely calculable in ways that the fully ∞-categorical theory is not, and I believe this computational accessibility may be a genuine advantage worth exploiting further." Il est ouvert à des directions ver HoTT par exemple (mais n'y connait aps grand chose) et tout ce qui est higher categorical. Grégory

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GdT demain
by Groupe de travail catégories 03 Apr '26

03 Apr '26

Hi! Tomorrow at 10:30am in B107, Léo Bartoli will talk to us about relative topos theory. Jonas and Quentin have told me they can't make it and I will need to leave as soon as the session is over, so please come if you are able to make up the numbers :) I'll send the BBB link in the morning. Best, Morgan

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GdT demain
by Groupe de travail catégories 27 Mar '26

27 Mar '26

Hi, Yiming asked me to tell you that her talk will actually mostly be about sheaf topoi and maps between them; Leo will tell us more about relative topos theory next week. See you tomorrow! Best wishes, Morgan

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My talk yesterday, GdT this week
by Groupe de travail catégories 26 Mar '26

26 Mar '26

Hi! In case you missed it, here is a link to my talk yesterday: https://www.youtube.com/watch?v=0d9O7W42zHw And a link to the BBB where you can find Ulrich's first talk: https://bbb.math.univ-paris13.fr/b/chr-hyw-0rb-jz4 This Friday at 10:30am in B107, Yiming Xu will talk to us about relative topos theory. I hope to see many of you there! Best wishes, Morgan

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Talk at the NYC category theory seminar
by Groupe de travail catégories 25 Mar '26

25 Mar '26

Fyi I'm speaking from now! See you there, maybe. Morgan

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Re: [GdT Categories] visite Ulrik BUCHHOLTZ & mini-course HoTT
by Groupe de travail catégories 22 Mar '26

22 Mar '26

Bonsoir, Ulrik Buchholtz’s HoTT mini-course is scheduled for the next three Wednesdays (March 25, April 1, and April 8), from 16:00 to 18:00 at Paris 13 University in Villetaneuse. The abstract is below. The room will be announced soon. We look forward to seeing many of you, and please feel free to forward this announcement. Best regards, Jonas Title : Introduction to Synthetic Homotopy Theory Abstract : We'll cover topics in synthetic homotopy theory using homotopy type theory/univalent foundations. First, we'll give a brief overview of Martin-Löf type theory and an intuitive picture of its interpretation in spaces qua infinity-groupoids. This interpretation motivates Voevodsky's definition of contractible types, equivalences, homotopy n-types, n-connected types, and the univalence axiom. Next, we cover homotopy pushouts as a new type constructor, including variations such as the circle, suspensions, cofibers, joins, and smash products. We'll look at the type-theoretic formulation of homotopy groups, and the long exact sequence given by a map, leading to the calculation of some homotopy groups. The last lecture will cover the zigzag construction of the path spaces of pushouts, leading to a type-theoretic proof of the Blakers–Massey connectivity theorem. Time permitting, we can touch on other aspects of synthetic homotopy theory, according to the interests of the participants. On 3/17/26 16:15, Jonas Frey wrote: > > Bonjour, > > Notre invité *Ulrik Buchholtz* arrivera lundi prochain (23 mars) et > restera jusqu'au 26 avril avec une interruption d'une semaine (du 12 > au 18 avril). En tant qu'invité de l'EUR > <https://eur.univ-paris13.fr/> il donnera un mini-cours d'environ > trois séances sur la *théorie homotopique de types* (HoTT) destiné aux > étudiants de master, mais aussi aux doctorants, postdocs et > permanents. Si ça vous intéresse vous et invités à remplir ce sondage > <https://lettucemeet.com/l/KwWpn> pour indiquer vos disponibilités. > > Dear all, > > Our guest *Ulrik Buchholtz* will be arriving next Monday (*March 23*) > and will be staying until *April 26*, with a one-week break from April > 12 to 18. As a guest of the EUR <https://eur.univ-paris13.fr/>, he > will give a mini-course of about three sessions on *Homotopy Type > Theory (HoTT)*. This course is *aimed at* Master’s students, but PhD > students, postdocs, and permanent staff are also welcome to attend. > > If you are interested, you are invited to fill out this poll > <https://lettucemeet.com/l/KwWpn> to indicate your availability. > > Best, > > Jonas >

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GdT demain
by Groupe de travail catégories 20 Mar '26

20 Mar '26

Hi! It's been plenty of time, so even with no specific plan, I'll announce that we'll have a GdT tomorrow in B107 at 10:30am as usual. If Christian can't do the talk which was planned for last week that we had to cancel, maybe I'll tell you all about my understanding of relative monads! I'll set up the BBB at the usual link too. Best wishes, Morgan

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