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Anny Beatriz Azevedo (she/her) (Sep 25 2026 at 23:39):Dear all,
We are pleased to announce the Brazilian Category Theory seminars of this semester, with monthly talks. We invite everyone to join us for our next meeting, which will take place next Monday, September 28, at 4:00 PM (SP time).
Fernando Yamauti (USP)
September 28, 2026 – 4:00 PM (SP time)
Online at: https://meet.google.com/ruk-zppv-jtu
Title: Topoi and Homotopy Types
Abstract: The main result of the classic monograph "Classifying Spaces and Classifying Topoi" by Moerdijk states that presheaf topoi C^ present the homotopy type of the classifying space BC. I will present a new proof for general (oo,1)-topoi as well as point some consequences of the localisation techniques used in this proof. If time remains, I will point some ongoing work on computations of related localisations of the category Topos.
For more information about other seminars, events, and category theory projects in Brazil, visit our website: https://categorias-brasil.github.io/.
Anny Beatriz Azevedo (she/her) (Nov 06 2026 at 17:34):Dear all,
We are pleased to announce the next Brazilian Category Theory seminar. We invite everyone to join us next Monday, November 09, at 4:00 PM (SP time).
Wilmer Leal (University of Florida)
November 09, 2026 – 4:00 PM (SP time)
Online at: https://meet.google.com/thb-dxqu-ipw
Title: An Invitation to Narratives: Sheaf-Theoretic Models of Time-Varying Systems
Abstract: Many of the systems we seek to understand, from evolving datasets and dynamic networks to autonomous multi-agent systems, are inherently temporal. Yet the mathematical tools used to study temporal phenomena are often developed in isolation within particular disciplines, making it difficult to identify shared principles and transfer insights across domains. In this talk, I will introduce narratives, a sheaf-theoretic framework for modeling time-varying objects of arbitrary mathematical type. Narratives provide a common language for organizing temporal data, comparing different representations of evolving systems, and studying how information changes through time.
The talk will be guided by three motivating questions. First, what information is preserved or lost when we pass between different representations of temporal data? Second, how can time-varying objects be decomposed into simpler components, and which invariants capture their structural complexity? Third, how can such abstract constructions be used in practice, for instance to model multi-agent systems whose communication networks change over time? Through these examples, we will see how sheaf-theoretic and categorical methods offer a unifying perspective on problems that arise across mathematics, data science, and control theory.
This talk is based on the paper Time-Varying Data as Sheaves: an Invitation to Narratives by Wilmer Leal, Benjamin Merlin Bumpus, Jana K. Nickel, Johan García, James Fairbanks, and Warren Dixon.
For more information about other seminars, events, and category theory projects in Brazil, visit our website: https://categorias-brasil.github.io/.