![[Oxford Seminar] David Corfield | Charles Peirce, inference, and category theory @ToposInstitute](https://i.ytimg.com/vi/c6-rGLK1Mps/sddefault.jpg)
Uploaded March 2025 | Updated September 2026, 2 weeks ago
Oxford Seminar, 20th of February 2025
The American philosopher Charles Saunders Peirce (1839-1914) had much to say about the nature of intellectual enquiry. In the realm of deductive logic, category theorists have made important use of his string-diagrammatic logical calculus. But Peirce's interests in inference extended beyond deduction to induction and abduction. In this talk I shall be exploring the thesis that we can understand this triple in terms of the category-theoretic notions of composition, extension and lift. We will also touch on his broader semiotics and his account of concept formation.
Oxford Seminar, 20th of February 2025
The American philosopher Charles Saunders Peirce (1839-1914) had much to say about the nature of intellectual enquiry. In the realm of deductive logic, category theorists have made important use of his string-diagrammatic logical calculus. But Peirce's interests in inference extended beyond deduction to induction and abduction. In this talk I shall be exploring the thesis that we can understand this triple in terms of the category-theoretic notions of composition, extension and lift. We will also touch on his broader semiotics and his account of concept formation.
![[Oxford Seminar] David Corfield | Charles Peirce, inference, and category theory](https://i.ytimg.com/vi/c6-rGLK1Mps/mqdefault.jpg "[Oxford Seminar] David Corfield | Charles Peirce, inference, and category theory
Oxford Seminar, 20th of February 2025
The American philosopher Charles Saunders Peirce (1839-1914) had much to say about the nature of intellectual enquiry. In the realm of deductive logic, category theorists have made important use of his string-diagrammatic logical calculus. But Peirces interests in inference extended beyond deduction to induction and abduction. In this talk I shall be exploring the thesis that we can understand this triple in terms of the category-theoretic notions of composition, extension and lift. We will also touch on his broader semiotics and his account of concept formation.")
![[Berkeley Seminar] Gabriel Goren-Roig | Arboreal coreflections](https://i.ytimg.com/vi/cBtySZMrtgA/mqdefault.jpg "[Berkeley Seminar] Gabriel Goren-Roig | Arboreal coreflections
Title: Arboreal coreflections
Abstract: Arboreal categories are categories of objects with an intrinsic, tree-like process structure giving rise to a bisimilarity relation between objects. This relation can then be transported along an adjunction into an “extensional” category, whose objects are usually relational structures. In this way, the main examples of these so-called arboreal adjunctions recover logical equivalence for various fragments of infinitary first-order logic. This abstract framework provides a solid foundation for game comonads and has been used to obtain extensions and variations of substantial resource-sensitive model-theoretic results such as Rossman’s equirank preservation theorem. However, a key open question is whether we can systematically chart the landscape of the correspondence between logics and arboreal adjunctions.
In this talk, we explore this landscape by focusing on coreflective arboreal adjunctions. As is well known, the theory of (co)monads simplifies greatly in the idempotent case and, accordingly, known idempotent game comonads correspond to variants of basic modal logic, which sit on the lower end of the expressive power spectrum. After reviewing the definition of arboreal categories, we will introduce the concept of a “seed”: a full subcategory of structures generating an arboreal coreflective subcategory via colimit. We will explain some results that help us identify seeds and hence move towards a potential classification theorem. In particular, we will leverage density comonads to characterize coreflective subcategories without explicitly constructing the coreflector. Finally, we will show some examples of arboreal categories that can be obtained employing our results.
Date: July 2, 2025
https://topos.institute/events/berkeley-seminar/")
![[Oxford Seminar] Virginie Debauche | The Path-Complete Formalism for Switched Systems](https://i.ytimg.com/vi/cckhqPmiVuw/mqdefault.jpg "[Oxford Seminar] Virginie Debauche | The Path-Complete Formalism for Switched Systems
Oxford Seminar, 17th of April 2025
TITLE: The Path-Complete Formalism for Switched Systems: Stability and Beyond
ABSTRACT: Switched systems play a crucial role in modern engineering thanks to their ability to capture complex behaviours involving transitions between different operational modes. However, analyzing their stability remains a challenging task due to the intricate interplay between discrete switching and dynamics. This complexity calls for sophisticated mathematical tools. While Lyapunov theory remains a cornerstone of stability analysis, traditional methods often fall short when applied to switched systems, prompting ongoing efforts to extend the theory to better accommodate their unique characteristics.
This talk presents the framework of path-complete Lyapunov functions, which offers a fresh perspective by integrating combinatorial structures to represent switching behaviour. Specifically, a path-complete Lyapunov function comprises two components: a combinatorial element, represented by an automaton (a directed graph) that encodes admissible switching sequences, and an algebraic element, consisting of a collection of Lyapunov functions—one for each node in the graph. The graph edges govern how these Lyapunov pieces interact and decrease across transitions. This framework is particularly appealing for the analysis of switched systems because it allows for the construction of tailored, nonstandard, and less conservative stability criteria, all while mitigating the combinatorial complexity that often burdens classical optimization techniques.
While originally introduced for stability analysis, the path-complete Lyapunov framework has been recently extended to encompass constrained switching systems, stabilization via switching sequence and control Lyapunov function design, and safety through path-complete barrier functions. This talk will highlight these recent developments and their unifying role within the framework.")
![[Oxford Seminar] Owen Lynch | An introduction to the geolog project](https://i.ytimg.com/vi/d6xMeIxsCM4/mqdefault.jpg "[Oxford Seminar] Owen Lynch | An introduction to the geolog project
Oxford Seminar, April 2 2026
Speaker: Owen Lynch
Full Title: An introduction to the geolog project
Abstract: Within the ARIA program, a number of researchers are working on a project called geolog. Geolog has some ambitious goals and some controversial theses; in this talk we will give an overview of these goals and theses alongside an intro to some of the math and computer science that we are using to attempt to achieve the goals and confirm the theses.")
![[2-torial] Categorical algebraic geometry, Part 2](https://i.ytimg.com/vi/dZKDEhOhz8E/mqdefault.jpg "[2-torial] Categorical algebraic geometry, Part 2
2-torial, July 28 2026
You can find accompanying notes and other information on this video at https://topos.institute/work/lectures/2-torials/2026-07-28_hosgood_geometry/
Speaker: Tim Hosgood
There are many approaches to algebraic geometry, and many different ways to arrive at the subject. Here were going to take an incredibly specific and biased approach: what if you already love 2-categories and want to be able to say the phrase fpqc sheaf as quickly as possible, but not /too/ quickly? In this series of exercises we will build towards an understanding of *relative algebraic geometry*, which allows us to work in arbitrary (nice) symmetric monoidal categories.")
![[DOTS Lectures] 9. Behavioural modules of systems](https://i.ytimg.com/vi/de20OAaAqW0/mqdefault.jpg "[DOTS Lectures] 9. Behavioural modules of systems
Part of a lecture series on the Double Operadic Theory of Systems (DOTS) presented by David Jaz Myers.
Some material from these lectures can be found in Davids book on categorical systems theory:
https://www.davidjaz.com/Papers/DynamicalBook.pdf")
![[Oxford Seminar] Elizabeth Amelia | AI for precision oncology](https://i.ytimg.com/vi/eDZuVRE-XVU/mqdefault.jpg "[Oxford Seminar] Elizabeth Amelia | AI for precision oncology
Oxford Seminar, 29th of May 2025")
![[TopOx] Jakub Opršal: Homotopy theory in the complexity of homomorphism problems](https://i.ytimg.com/vi/fU2pZbrE2aA/mqdefault.jpg "[TopOx] Jakub Opršal: Homotopy theory in the complexity of homomorphism problems
27th of November 2025. Slides available at https://topos.institute/events/topox/
I will talk about an emerging connection between homotopy theory and computational complexity of discrete problems. I will outline a theorem stating that contractibility is necessary for tractability (assumin P ≠ NP) in the realm of finite-template constraint satisfaction problems (CSPs).
There are many ways the CSP can be formulated. One of them is as a homomorphism problem: given two relational structures A and B, decide whether there is a homomorphism from A to B. We usually study a restricted version of this problem where B is fixed, e.g., if B is the k-clique graph K_k, the problem is the same as k-colouring of a given graph A. If B is finite (and of finite signature), such a problem is called finite-template. Famously, finite-template CSPs exhibit a P vs NP-complete dichotomy as proved independently by Bulatov and Zhuk in 2017.
The main theorem of the talk states a sufficient condition for NP-completeness in terms of the topology of ‘solution spaces’ and provides both all necessary hardness for the Bulatov–Zhuk dichotomy and also a new proof of an earlier Hell–Nešetřil dichotomy of graph homomorphism problems.")
