The New York City
Category Theory Seminar
Department of Computer Science
Department of Mathematics
The Graduate Center of The City University of New York
THIS SEMESTER, SOME TALKS WILL BE IN-PERSON AND SOME WILL BE ON ZOOM.
Time: Wednesdays 07:00 PM Eastern Time (US and Canada)
IN-PERSON INFORMATION:
365 Fifth Avenue (at 34th Street) map
(Diagonally across from the Empire State Building)
New York, NY 10016-4309
Room 6496
The videos of the lectures will be put up on YouTube a few hours after the lecture.
ZOOM INFORMATION:
https://brooklyn-cuny-edu.zoom.us/j/81090491347?pwd=NnbAzAnuh70bxYsEmhJSPfxoGIP0aN.1
Meeting ID: 810 9049 1347
Passcode: 706111
Seminar web page.
Videoed talks.
Previous semesters.
List of previous speakers.
Researchseminars.org page.
Contact N. Yanofsky to
schedule a speaker
or to add a name to the
seminar mailing list.
Fall 2025
Speaker: TBA, TBA.
Date and Time: Wednesday September 10, 2025, 7:00 - 8:30 PM.
Title: TBA.
Abstract: TBA
Speaker: Sam McCrosson, Montana State University.
Date and Time: Wednesday September 17, 2025, 7:00 - 8:30 PM. ZOOM TALK.
Title: Using Microsupports to Detect and Describe Constructible Sheaves.
Abstract: Microlocal sheaf theory has been gaining popularity recently for its applications to symplectic geometry. In this talk, we’ll explore a more topological application of this subject: how the notion of the microsupport of a sheaf can be used to tell if a sheaf is “constructible,” i.e. locally constant on strata, and if so, what the coarsest stratification is with this property.
Versions of this result can be found as far back as Kashiwara and Schapira’s 1990 book “Sheaves on Manifolds” (which pioneered the subject of microlocal sheaf theory). Today, all sorts of generalizations are possible using schemes, \infty-categories, and other fancy machinery. This talk will focus on a particularly simple case: using 1-category theory and sheaves of sets on topological spaces to illustrate the key ideas with concrete examples.
Speaker: Amartya Shekhar Dubey, National Institute of Science Education and Research.
Date and Time: Wednesday October 22, 2025, 2:00 - 3:00 PM. New York time. ZOOM TALK
Title: Unital k-restricted Infinity Operads.
Abstract: The goal is to understand unital \infty-operads by their arity restrictions. Given k \geq 1, we develop a model for unital k-restricted \infinty-operads, which are variants of \infinity-operads with (\leq k)-arity morphisms, as complete Segal presheaves on closed k-dendroidal trees built from corollas with valence \leq k. Furthermore, we prove that the restriction functors from unital \infty-operads to unital k-restricted \infty-operads admit fully faithful left and right adjoints by showing that the left and right Kan extensions preserve complete Segal objects. Varying k, the left and right adjoints give a filtration and a co-filtration for any unital \infty-operads by k-restricted \infty-operads. This is joint work with Yu Leon Liu.
Speaker: Jonathon Funk, Queensborough, CUNY.
Date and Time: Wednesday October 29, 2025, 7:00 - 8:30 PM. IN-PERSON TALK
Title: Toposes and C*-algebras.
Abstract: TBA
Speaker: Florian Lengyel, CUNY.
Date and Time: Wednesday November 5, 2025, 7:00 - 8:30 PM. ZOOM TALK
Title: Horn-filling thresholds in simplicial tensor modules.
Abstract: Let \( R \) be a PID and let \( \vec{s} = (n_1, \dots, n_k) \) be a "shape" vector with \( k, n_i \ge 2 \).
Write \( X_\bullet(\vec{s}) \) for the simplicial \( R \)-module generated by tensors of shape \( \vec{s} \),
where the simplicial structure is induced by diagonal application of the usual coface and codegeneracy operators along all axes;
set \( n = \min(\vec{s}) - 1 \).
For a nondegenerate \( n \)-simplex \( T \) (with nondegenerate boundary, i.e., no face \( d_i T \) lies in the degenerate submodule)
and \( 0 \le j \le n \), let \( \Lambda^n_j(T) \) be the corresponding horn and let \( L_\bullet \) denote the simplicial submodule
generated by the faces of the horn.
Using the standard fact that the set of fillers of \( \Lambda^n_j(T) \) is a torsor under
\[
R_{n,j} = \bigcap_{i \ne j} \ker\!\left(d_i : X_n(\vec{s}) \to X_{n-1}(\vec{s})\right),
\]
we show that \( \operatorname{rank}_R R_{n,j} \) admits an explicit inclusion–exclusion formula counting the “missing indices.”
In particular, non-unique fillers occur iff \( k \ge n \).
Under the Dold–Kan correspondence, the relative homology
\[
H_n\left(N(X_\bullet(\vec{s})), N(L_\bullet)\right)
\]
is the quotient of \( R_{n,j} \) by the image of the normalized boundary \( \partial_{n+1} \),
and is nontrivial iff \( k \ge n+1 \); when nontrivial its rank equals the missing–index count.
I will present the combinatorial formula, and accompanying code that verifies the counts and the two dichotomies.
Speaker: Emilio Minichiello, CUNY CityTech..
Date and Time: Wednesday November 12, 2025, 7:00 - 8:30 PM. IN-PERSON TALK.
Title: Model Structures for Simplicial Complexes and Graphs.
Abstract: I’ll talk about my new paper which constructs model structures on the category of simplicial complexes and on reflexive graphs which are reminiscent of the Thomason model structure on categories. I’ll give some background and motivation for studying this and the surrounding questions of graph homotopy theory.
Speaker: Raymond Puzio.
Date and Time: Wednesday November 26, 2025, 7:00 - 8:30 PM. IN-PERSON TALK
Title: The Krohn-Rhodes theorem.
Abstract: TBA
Speaker: TBA, TBA.
Date and Time: Wednesday December 3, 2025, 7:00 - 8:30 PM. IN-PERSON TALK
Title: TBA.
Abstract: TBA
Spring 2026
Speaker: TBA, TBA.
Date and Time: Wednesday February ??, 2026, 7:00 - 8:30 PM. IN-PERSON TALK
Title: TBA.
Abstract: TBA
Speaker: TBA, TBA.
Date and Time: Wednesday February ??, 2026, 7:00 - 8:30 PM. IN-PERSON TALK
Title: TBA.
Abstract: TBA
Speaker: TBA, TBA.
Date and Time: Wednesday February ??, 2026, 7:00 - 8:30 PM. IN-PERSON TALK
Title: TBA.
Abstract: TBA
Speaker: TBA, TBA.
Date and Time: Wednesday March ??, 2026, 7:00 - 8:30 PM. IN-PERSON TALK
Title: TBA.
Abstract: TBA
Speaker: TBA, TBA.
Date and Time: Wednesday March ??, 2026, 7:00 - 8:30 PM. IN-PERSON TALK
Title: TBA.
Abstract: TBA
Speaker: TBA, TBA.
Date and Time: Wednesday March ??, 2026, 7:00 - 8:30 PM. IN-PERSON TALK
Title: TBA.
Abstract: TBA
Speaker: TBA, TBA.
Date and Time: Wednesday April ??, 2026, 7:00 - 8:30 PM. IN-PERSON TALK
Title: TBA.
Abstract: TBA
Speaker: TBA, TBA.
Date and Time: Wednesday April ??, 2026, 7:00 - 8:30 PM. IN-PERSON TALK
Title: TBA.
Abstract: TBA