New York Combinatorics Seminar

This seminar is sponsored by the CUNY Graduate Center's Math Department and Computer Science Department. It covers a wide range of topics in combinatorics and its applications.  Talks are posted on our YouTube channel https://youtube.com/@NYCombinatorics and catalogued on the page Previous Semesters.

Time: Fridays 12:00 pm:  1:00 pm ET (Eastern Time)
Location: The CUNY Graduate Center is located at 365 Fifth Avenue (at the corner of 34th Street), New York. It can be easily reached by subway using the B,D,F,N,Q,R, or 6 train.

Seminar Co-Organizers (alphabetically):  Kira Adaricheva (Hofstra University) Deepak Bal (Montclair State University) Nadia Benakli (City Tech) Jonathan Cutler (Montclair State) Ezra Halleck (City Tech), Sandra Kingan (Graduate Center & Brooklyn College), Joseph Malkevitch (Graduate Center & York College), Kerry Ojakian (BCC), Megan Owen (Graduate Center & Lehman College),  Jinyoung Park (New York University), Anna Pun (Graduate Center & Baruch College), Eric Ramos (Stevens Institute of Technology), (Abigail Raz (Cooper Union), Eric Rowland (Hofstra University), Mingxian Zhong (Graduate Center & Lehman College).

Lead Organizer:
2025 - 2026: Deepak Bal
2024 - 2025: Anna Pun
2011 - 2024: Sandra Kingan

SPRING 2026 TALKS

Room for In-person talks: Graduate Center 9116

Zoom link: https://montclair.zoom.us/j/93937899930?pwd=t3CoLts4pfRXcmhpUsUI6fIys9nv0p.1
Meeting ID: 93937899930     Passcode nycs

Feb 6:  Sandra Kingan (Brooklyn College and The Graduate Center) (virtual)

Title:  Deletable edges in 3-connected graphs and their applications

Abstract: In this talk I will analyze 3-connected graphs that contain a fixed 3-connected graph 𝐻 as a minor, but in which no edge can be deleted while preserving 3-connectivity and an 𝐻-minor. Let G and H be simple 3-connected graph such that G has an H-minor.  An edge e in G is called H-deletable if G\e is 3-connected and has an H-minor.  If G has no H-deletable edge, then G can be reduced to H using three specific local operations.  This gives a framework for studying extremal graphs with no 𝐻-deletable edges and yields applications to excluded-minor questions. This talk is based on a paper that just appeared in Discrete Mathematics (https://doi.org/10.1016/j.disc.2026.114994)
 

Feb 13:  No Talk

Feb 20:  Aditya Khanna (Virginia Tech) (in person)

Title: Proving two matrices are inverses using pictures

Abstract: Many objects in combinatorics can be constructed recursively, and we can associate signed weights to these constructed objects. We record these signed weights in a “combinatorial” matrix where any entry of the matrix sums over all objects of a certain prescription. Natural examples of such combinatorial matrices are change-of-basis matrices in the study of symmetric functions. In this talk, we discuss how the condition that two combinatorial matrices are inverses can be understood entirely in terms of local operations on the combinatorial objects the matrices record. We then show how these local rules can be used to give canonical combinatorial proofs that the matrices are mutually inverse. We will illustrate these ideas using one of the most important examples in symmetric functions, the Kostka matrix $K$, and display an elegant, canonical bijection establishing $KK^{-1} = I$. The framework described in the talk is general, and applicable beyond symmetric function theory. There are no prerequisites, and all algebraic and combinatorial concepts will be defined in the talk. 

Feb 27: John Byrne (University of Delaware) (in person)

Title: Directed even cycles and nonabelian Sidon sets

Abstract: It is a deep and long-standing open question whether there exist $n$-vertex graphs with $cn^{1+1/k}$ edges and no cycle of length $2k$. In this talk I will discuss variants of this question for directed graphs. In particular, we study minimum degree conditions which guarantee the existence of a given orientation of the $2k$-cycle. We present a construction which shows how this problem depends strongly on the number and orientation of the forbidden cycles, as well as an application of this construction to an extremal problem about permutations. When restricting this problem to Cayley graphs, one seeks a nonabelian variant of Sidon sets, and we also obtain lower and upper bounds on the maximum size of such objects. This talk is based on joint work with Michael Tait. (https://arxiv.org/abs/2509.07750)

Mar 6: Alex Nowak (Howard University)

Title: Cyclic designs and the set-theoretical Yang-Baxter equation

Abstract: First appearing in the field of statistical mechanics in the mid-twentieth century, the quantum Yang-Baxter equation has since become essential to our understanding of knots, braids, and quantum groups. To make the problem of classifying solutions more tractable, Drinfeld proposed the study of the stripped-down, combinatorial version: a map r : Q^2 -> Q^2 is a solution to the set-theoretical Yang-Baxter equation if (r x 1_Q)(1_Q x r)(r x 1_Q)=(1_Q x r)(r x 1_Q)(1_Q x r).$ While the best-understood solutions are involutive ($r^2=1_{Q^2}$) and, more generally, of even order, in this talk, we are going to focus on odd-order solutions, with an emphasis on those of order 3. We will show that to each order-3 solution, one can associate a Mendelsohn triple system (a cyclic generalization of a Steiner triple system). This greatly restricts the possible sizes of the underlying set Q. We will also discuss a class of solutions whose structure is entirely determined by the automorphism group of the associated triple system. This is joint work with Anna Zamojska-Dzienio. (https://arxiv.org/abs/2504.06555)  

Mar 13:  

Mar 20: must be virtual

Mar 27:  Mina Rees NY Women in Math Conference

Apr 3: Cicely Henderson (virtual)

Apr 10:  Anthony Christiana (virtual)

Apr 17: Emilio Minichiello

Apr 24: Athar Abdul-Quader

May 1: Robert Donley (in person)

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Previous Speakers:
Fall 2025
Spring 2025
Fall 2024
Spring 2024
Fall 2023
Spring 2023
Fall 2022
Spring 2022
Fall 2021
Spring 2021
Fall 2020
Spring 2020
Fall 2019
Spring 2019
Fall 2018
Spring and Summer 2018
Fall 2017
Spring 2017
Fall 2016
Spring 2016
Fall 2015
Spring 2015
Fall 2014
Spring 2014
Fall 2013
Spring 2013
Fall 2012
Spring 2012
Fall 2011
Spring 2011
Previous Talks hosted by Janos Pach

Previous Organizers:
Christopher Hanusa (2011 - 2015)