Young Researchers in Extremal and Probabilistic Combinatorics
2021-10-20 - 2021-10-22 | Zoom ID: 554 788 7710 (507464)
The aim of the Young Researchers in Extremal and Probabilistic Combinatorics is to bring together early career researchers working on these topics. The workshop will consist of several 25 minute talks across three days from October 20 to 22, 2021. Due to Covid the workshop will be held online.

Invited Speakers & Program
Oct. 20 Wednesday 4 PM (KST) – 8 PM (KST)

Andrzej Grzesik (Jagiellonian University): Degenerated generalized Turán numbers of cycles, 4:00-4:25
Jan Volec (Czech Technical University): Existence of common graphs with large chromatic number, 4:30-4:55
Balázs Patkós (Rényi Institute): Vector sum-intersection theorems, 5:00-5:25
István Tomon (ETH Zurich): Small doubling, atomic structure and $ell$-divisible set families, 5:30-5:55
Michael Anastos (Freie Universität Berlin): Longest Cycles in Sparse Random Graphs and Where to Find Them, 6:30-6:55
Adam Zsolt Wagner (Tel Aviv University): Constructions in combinatorics via neural networks, 7:00-7:25
Yelena Yuditsky (Université libre de Bruxelles): On multicolor Ramsey numbers and subset-coloring of hypergraphs, 7:30-7:55

Oct. 21 Thursday 4 PM (KST) – 8 PM (KST)

Kevin Hendrey (IBS Discrete Mathematics Group): Extremal functions for sparse minors, 4:00-4:25
Simona Boyadzhiyska (Freie Universität Berlin): Ramsey simplicity of random graphs, 4:30-4:55
Shagnik Das (National Taiwan University): Schur’s Theorem in randomly perturbed sets, 5:00-5:25
Tony Huynh (Monash University): Subgraph densities in minor-closed classes (and beyond), 5:30-5:55
Ander Lamaison (Masaryk University): Hypergraphs with minimum uniform Turán density, 6:30-6:55
Ben Lund (IBS Discrete Mathematics Group): Maximal 3-wise intersecting families, 7:00-7:25
Liana Yepremyan (London School of Economics): Enumerating independent sets in Abelian Cayley graphs, 7:30-7:55

Oct. 22 Friday 4 PM (KST) – 8 PM (KST)

Andrey Kupavskii (CNRS): Binary scalar products, 4:00-4:25
Dániel Gerbner (Rényi Institute): Exact results for generalized Turán problems, 4:30-4:55
Oliver Janzer (University of Cambridge): Tiling with monochromatic bipartite graphs of bounded maximum degree, 5:00-5:25
Nika Salia (Rényi Institute): Pósa-type results for Berge Hypergraphs, 5:30-5:55
Debsoumya Chakraborti (IBS Discrete Mathematics Group): Mixing time and expanders, 6:30-6:55
Wei-Tian Li (National Chung Hsing University): Ramsey Properties for $V$-shaped Posets in the Boolean Lattices, 7:00-7:25
Dimitry Zakharov (Moscow Institute of Physics and Technology): Zero subsums in vector spaces over finite fields, 7:30-7:55

Abstracts (pdf file)

Graph Product Structure Theory: Gathering of Participants from Korea
2021-11-23 - 2021-11-26 | Room B223, IBS (기초과학연구원)
On November 22-26, 2021, there is a “Graph Product Structure Theory” workshop in BIRS Centre in Banff (https://www.birs.ca/events/2021/5-day-workshops/21w5235), organized in a hybrid manner with 15 onsite participants and around 50 remote participants. We would like to meet in a group of 5-10 remote participants from Korea in one place, creating a secondary workshop site in Korea. This would allow joint participation in online talks and in-person discussions between local participants.

2021 Combinatorics Workshop (2021 조합론 학술대회)
2021-12-20 - 2021-12-22 | The Bloomvista
The Combinatorics Workshop (조합론 학술대회) is an annual conference of combinatorialists in Korea that started in 2004 by the Yonsei University BK21 Research Group. Since 2013, this workshop has been advised by the committee of discrete mathematics of the Korean Mathematical Society. This year it will take place at The Bloomvista in Yangpyeong on December 20-22, 2021.
The aim of this workshop is to bring together active researchers with different backgrounds to discuss recent and prospective advances in combinatorics and related areas.
We plan to limit the number of participants. Registration (without a fee) will be required. General participants will be required to pay for their own accommodation.

Title: 2021 Combinatorics Workshop (2021 조합론 학술대회)
Date: December 20 – 22 (Mon-Wed), 2021
Venue: The Bloomvista, Yangpyeong
Website: https://cw2021.combinatorics.kr

Plan

Starting in the afternoon of Thursday and ending in the morning of Wednesday.
There will be 5 invited talks for 50 minutes each.
There will be contributed talks for 25 minutes each.

Using English is recommended if there are non-Korean participants in the audience.
The call for contributed talks will be announced later.

It will be an offline meeting.

Invited Speakers

Dongsu Kim, KAIST
Joonkyung Lee, Hanyang University
Hong Liu, University of Warwick, UK
Suil O, SUNY Korea
Seonjeong Park, Jeonju University

Call for Abstracts
We are looking for contributed talks! If you are interested in giving a contributed talk, then please submit your abstract until November 15, 2021.
Registration

Please fill out the registration form by November 21, 2021.

The registration is free.
The organizers will announce the price for the accommodation soon.

Due to the government COVID-19 policy, the organizers may reject some registration, even if the registration was made before November 21.

Organizing Committee

Jeong-Ok Choi, GIST
Sang-il Oum, IBS Discrete Mathematics Group and KAIST
Heesung Shin, Inha University

Advisory Committee
Committee of Discrete Mathematics, The Korean Mathematical Society (Chair: Soojin Cho, Ajou University)
Host and Sponsors
IBS Discrete Mathematics Group

MATRIX-IBS Workshop: Structural Graph Theory Downunder II
2022-03-20 - 2022-03-27 | MATRIX, Australia
This program consists of a short intensive workshop, where mathematicians from across the globe will come together to work on open problems in structural graph theory. We will consider the following research themes: graph minors, graph colouring, Hadwiger’s Conjecture, bounded expansion classes, graph product structure theory, generalised colouring numbers, VC dimension, induced subgraphs, Erdős-Hajnal conjecture, Gyárfás-Sumner conjecture, twin-width, asymptotic dimension. The majority of the time will be allocated to collaborative research (with only a few talks). The goal is to create an environment where mathematicians at all career stages work side-by-side. We anticipate that open problems will be solved, and lasting collaborations will be initiated.
URL: https://www.matrix-inst.org.au/events/structural-graph-theory-downunder-ll/
Registration is by invitation only. If you are interested to participate in this research program, please contact one of the organisers with your CV and research background.

IBS ECOPRO Opening conference
2022-04-04 - 2022-04-06 | Zoom ID: 878 0445 3986 (ibsecopro) [CLOSED]
To celebrate the opening of the IBS ECOPRO (Extremal Combinatorics and Probability) Group, we will organize a 3-day online conference from April 4 to April 6.
Official Website: https://www.ibs.re.kr/ecopro/event/opening/
Invited Speakers

Noga Alon
Princeton University

József Balogh
University of Illinois at Urbana-Champaign

Jeff Kahn
Rutgers University

Mihyun Kang
Graz University of Technology

Jeong Han Kim
KIAS

Nati Linial
Hebrew University of Jerusalem

Oleg Pikhurko
University of Warwick

Benny Sudakov
ETH Zürich

Tibor Szabó
Freie Universität Berlin

Van Vu
Yale

Program

Time in Korea
Monday
Tuesday
Wednesday

7:15 PM
Kim

8:00 PM
Pikhurko
Kang
Vu

8:45 PM
Kahn
Balogh
Szabó

9:30 PM
Alon
Sudakov
Linial

Organizers

Jaehoon Kim, KAIST
Hong Liu, IBS Extremal Combinatorics and Probability Group
Sang-il Oum, IBS Discrete Mathematics Group / KAIST
Tuan Tran, IBS Discrete Mathematics Group

KSIAM 2022 Spring Meeting
2022-05-27 13:20 - 17:40 (Asia/Seoul) | IBS Science Culture Center
KSIAM (Korean Society for Industrial and Applied Mathematics) will have the KSIAM 2022 Spring Conference at the Institute for Basic Science (IBS). Its academic session for Combinatorics decided to have an invited talk by Joonkyung Lee at the Hanyang University, a special session “Graph Theory” organized by Sang-il Oum and the IBS DIMAG, a special session “Enumerative Combinatorics” organized by Dongsu Kim at KAIST, and a poster session, all on May 27 afternoon. The deadline for the abstract submission is May 2 and the deadline for the early registration is May 9.
Invited talk (May 27 Friday, 16:40-17:40)

Joonkyung Lee이준경 (Hanyang University), Graph homomorphism inequalities and their applications
Counting (weighted) homomorphisms between graphs relates to a wide variety of areas, in- cluding graph theory, probability, statistical physics and theoretical computer science. In recent years, various new applications of inequalities between graph homomorphism counts have been found.
We will discuss some of the examples, including a simple proof of the Bondy–Simonovits theorem and a new estimate for the rainbow Turán numbers of even cycles. If time permits, we will also touch upon some recent progress on Sidorenko’s conjecture and related questions, in particular their applications on the bipartite Turán problems.
Based on joint work with David Conlon, Jaehoon Kim, Hong Liu, and Tuan Tran.

Special session “Graph Theory” (May 27, 13:20-14:40)
Organized by Sang-il Oum엄상일 (IBS Discrete Mathematics Group & KAIST).
Speakers

Boram Park박보람 (Ajou University), Odd Coloring of Graphs
An odd $c$-coloring of a graph is a proper $c$-coloring such that each non-isolated vertex has a color appearing an odd number of times on its neighborhood. Recently, Cranston investigated odd colorings of graphs with bounded maximum average degree, and conjectured that every graph $G$ with $operatorname{mad}(G)leq frac{4c-4}{c+1}$ has an odd $c$-coloring for $cgeq 4$, and proved the conjecture for $cin{5, 6}$. In particular, planar graphs with girth at least $7$ and $6$ have an odd $5$-coloring and an odd $6$-coloring, respectively.
We completely resolve Cranston’s conjecture. For $cgeq 7$, we show that the conjecture is true, in a stronger form that was implicitly suggested by Cranston, but for $c=4$, we construct counterexamples, which all contain $5$-cycles. On the other hand, we show that a graph $G$ with $operatorname{mad}(G)<frac{22}{9}$ and no induced $5$-cycles has an odd $4$-coloring. This implies that a planar graph with girth at least 11 has an odd $4$-coloring. We also prove that a planar graph with girth at least 5 has an odd $6$-coloring.
Joint work with Eun-Kyung Cho, Ilkyoo Choi, and Hyemin Kown.

Jongyook Park박종육 (Kyungpook National University), On the Delsarte bound
We study the order of a maximal clique in an amply regular graph with a fixed smallest eigenvalue by considering a vertex that is adjacent to some (but not all) vertices of the maximal clique. As a consequence, we show that if a strongly regular graph contains a Delsarte clique, then the parameter μ is either small or large. Furthermore, we obtain a cubic polynomial that assures that a maximal clique in an amply regular graph is either small or large (under certain assumptions). Combining this cubic polynomial with the claw-bound, we rule out an infinite family of feasible parameters (v, k, λ, μ) for strongly regular graphs. Lastly, we provide tables of parameters (v, k, λ, μ) for nonexistent strongly regular graphs with smallest eigenvalue −4,−5,−6 or −7. This is joint work with Gary Greaves and Jack Koolen.

O-joung Kwon권오정 (Hanyang University and IBS Discrete Mathematics Group), Well-partitioned chordal graphs
We introduce a new subclass of chordal graphs that generalizes the class of split graphs, which we call well-partitioned chordal graphs. A connected graph $G$ is a well-partitioned chordal graph if there exist a partition $mathcal{P}$ of the vertex set of $G$ into cliques and a tree $mathcal{T}$ having $mathcal{P}$ as a vertex set such that for distinct $X,Yin mathcal{P}$, (1) the edges between $X$ and $Y$ in $G$ form a complete bipartite subgraph whose parts are some subsets of $X$ and $Y$, if $X$ and $Y$ are adjacent in $mathcal{T}$, and (2) there are no edges between $X$ and $Y$ in $G$ otherwise. A split graph with vertex partition $(C, I)$ where $C$ is a clique and $I$ is an independent set is a well-partitioned chordal graph as witnessed by a star $mathcal{T}$ having $C$ as the center and each vertex in $I$ as a leaf, viewed as a clique of size $1$. We characterize well-partitioned chordal graphs by forbidden induced subgraphs, and give a polynomial-time algorithm that given a graph, either finds an obstruction, or outputs a partition of its vertex set that asserts that the graph is well-partitioned chordal.
We observe that there are problems, for instance Densest $k$-Subgraph and $b$-Coloring, that are polynomial-time solvable on split graphs but become NP-hard on well-partitioned chordal graphs. On the other hand, we show that the Geodetic Set problem, known to be NP-hard on chordal graphs, can be solved in polynomial time on well-partitioned chordal graphs. We also answer two combinatorial questions on well-partitioned chordal graphs that are open on chordal graphs, namely that each well-partitioned chordal graph admits a polynomial-time constructible tree $3$-spanner, and that each ($2$-connected) well-partitioned chordal graph has a vertex that intersects all its longest paths (cycles). Joint work with Jungho Ahn, Lars Jaffke, and Paloma T. Lima.

Stijn Cambie (IBS Extremal Combinatorics and Probability Group), Regular Cereceda’s Conjecture
The reconfiguration graph $mathcal C_k(G)$ for the $k$-colourings of a graph $G$ has a vertex for each proper $k$-colouring of $G$, and two vertices of $mathcal C_k(G)$ are adjacent precisely when those $k$-colourings differ on a single vertex of $G$. Much work has focused on bounding the maximum value of $operatorname{diam} mathcal C_k(G)$ over all $n$-vertex graphs $G$. One of the most famous conjectures related related to $mathcal C_k(G)$ is Cereceda’s conjecture, which says that if $k ge operatorname{degen}(G) + 2$, the diameter of $mathcal C_k(G)$ is $O(n^2)$. In this talk, we give some ideas towards a precise form for Cereceda’s conjecture, when restricting to regular graphs.
This is based on joint work with Wouter Cames van Batenburg (TU Delft, the Netherlands) and Daniel Cranston (Virginia Commonwealth University, USA), which originates from the online workshop Graph Reconfiguration of the Sparse Graphs Coalition.

Special session “Enumerative Combinatorics” (May 27, 15:00-16:20)
Organized by Dongsu Kim김동수 (KAIST).
Speakers

Meesue Yoo류미수 (Chungbuk National University), Combinatorial description for the Hall-Littlewood expansion of unicellular LLT and chromatic quasisymmetric polynomials
In this work, we obtain a Hall–Littlewood expansion of the chromatic quasisymmetric functions by using a Dyck path model and linked rook placements. By using the Carlsson–Mellit relation between the chromatic quasisymmetric functions and the unicellular LLT polynomials, this combinatorial description for the Hall–Littlewood coefficients of the chromatic quasisymmetric functions also gives the coefficients of the unicellular LLT polynomials expanded in terms of the modified transformed Hall–Littlewood polynomials. Joint work with Seung Jin Lee.

Donghyun Kim김동현 (Sungkyunkwan University), Combinatorial formulas for the coefficients of the Al-Salam-Chihara polynomials
The Al-Salam-Chihara polynomials are an important family of orthogonal polynomials in one variable $x$ depending on 3 parameters $alpha$, $beta$ and $q$. They are closely connected to a model from statistical mechanics called the partially asymmetric simple exclusion process (PASEP) and they can be obtained as a specialization of the Askey-Wilson polynomials. We give two different combinatorial formulas for the coefficients of the (transformed) Al-Salam-Chihara polynomials. Our formulas make manifest the fact that the coefficients are polynomials in $alpha$, $beta$ and $q$ with positive coefficients.

Jisun Huh허지선 (Ajou University), Combinatorics on bounded Motzkin paths and its applications
A free Motzkin path of length (n) is a lattice path which starts at ((0,0)) or ((0,1)), ends at ((n,0)), and has only up steps (u=(1,1)), down steps (d=(1,-1)), and flat steps (f=(1,0)). In addition, if a free Motzkin path starts at ((0,0)) and stays weakly above the (x)-axis, then it is called a Motzkin path. In this talk, we construct a bijection between (F(m,r,k)) and (M(m,r,k)), where (F(m,r,k)) is the set of free Motzkin paths of length (m+r) with (r) flat steps that are contained in the strip (-lfloor k/2 rfloor leq y leq lfloor (k+1)/2 rfloor) and (M(m,r,k)) is the set of Motzkin prefixed of length (m+r) with (r) flat steps that are contained in the strip (0 leq y leq k). Furthermore, we provide path interpretations of ordinary/self-conjugate (t)-core partitions with (m)-corners as an application.
This is joint work with Hyunsoo Cho, Hayan Nam, and Jaebum Sohn.

Jihyeug Jang장지혁 (Sungkyunkwan University), A combinatorial model for the transition matrix between the Specht and web bases
We introduce a new class of permutations, called web permutations. Using these permutations, we provide a combinatorial interpretation for entries of the transition between the Specht and web bases, which answers Rhoades’s question. Furthermore, we study enumerative properties of these permutations. Joint work with Byung-Hak Hwang and Jaeseong Oh.

The 2nd Workshop on Developments in Combinatorics
2022-11-28 - 2022-11-29 | Zoom ID: 346 934 4087 (202209)
Official website (with the abstract)
Online workshop “Developments in Combinatorics”

Invited Speakers
Nov. 28 Monday
Jie Han, Beijing Institute of Technology
15:30 Seoul, 14:30 Beijing, 06:30 UK, 07:30 EU
Joonkyung Lee (이준경), Hanyang University
16:10 Seoul, 15:10 Beijing, 07:10 UK, 08:10 EU
Lior Gishboliner, ETH Zürich
16:50 Seoul, 15:50 Beijing, 07:50 UK, 08:50 EU
Alex Scott, University of Oxford
17:40 Seoul, 16:40 Beijing, 08:40 UK, 09:40 EU
Dongyeap Kang (강동엽), University of Birmingham
18:20 Seoul, 17:20 Beijing, 09:20 UK, 10:20 EU
Nov. 29 Tuesday
Chong Shangguan, Shandong University
15:30 Seoul, 14:30 Beijing, 06:30 UK, 07:30 EU
Zdeněk Dvořák, Charles University
16:10 Seoul, 15:10 Beijing, 07:10 UK, 08:10 EU
Andrzej Grzesik, Jagiellonian University
16:50 Seoul, 15:50 Beijing, 07:50 UK, 08:50 EU
Imre Leader, University of Cambridge
17:40 Seoul, 16:40 Beijing, 08:40 UK, 09:40 EU
Jozef Skokan, The London School of Ecnomics and Political Science
18:20 Seoul, 17:20 Beijing, 09:20 UK, 10:20 EU
Organizers

Hong Liu
Guanghui Wang
Bingyu Luan

Sponsors

IBS Extremal Combinatorics and Probability Group
Shandong University

MATRIX-IBS Workshop: Structural Graph Theory Downunder III
2023-04-17 - 2023-04-24 | MATRIX, Australia
Website: https://www.matrix-inst.org.au/events/structural-graph-theory-downunder-iii/
Program Description:
This program, jointly organised by MATRIX and the Discrete Mathematics Group of the Korean Institute for Basic Science (IBS), builds on the “Structural Graph Theory Downunder” programs held at MATRIX in 2019 and 2022. In this short intensive workshop, mathematicians from across the globe will come together to work on open problems in structural graph theory. The focus will be on graph colouring, graph minors, induced subgraphs, and graph product structure theory. The majority of the time will be allocated to collaborative research, with only a few talks describing recent advances. The goal is to create an environment where mathematicians at all career stages work side-by-side. We anticipate that open problems will be solved, and lasting collaborations will be initiated.
Confirmed Participants:
Rutger Campbell (Institute for Basic Science, Korea)
Linda Cook (Institute for Basic Science, Korea)
James Davies (University of Cambridge, UK)
Marc Distel (Monash University, Australia)
Zdeněk Dvořák (Charles University, Czech Republic)
Bryce Frederickson (Emory University, USA)
António Girão (University of Oxford, UK)
Pascal Gollin (Institute for Basic Science, Korea)
Kevin Hendrey (Institute for Basic Science, Korea)
Robert Hickingbotham (Monash University, Australia)
Freddie Illingworth (University of Oxford, UK)
O-joung Kwon (Hanyang University, Korea)
Florian Lehner (University of Auckland, New Zealand)
Anita Liebenau (UNSW, Australia)
Chun-Hung Liu (Texas A&M, USA)
Rose McCarty (Princeton University, USA)
Lukas Michel (University of Oxford, UK)
Sang-il Oum (Institute for Basic Science and KAIST, Korea)
Michael Savery (University of Oxford, UK)
Alex Scott (University of Oxford, UK)
Raphael Steiner (ETH Zurich, Switzerland)
Jane Tan (University of Oxford, UK)
Sebastian Wiederrecht (Institute for Basic Science, Korea)
David Wood (Monash University, Australia)
Liana Yepremyan (Emory University, USA)

Open Symposium at the Discrete Mathematics Group
2023-07-13 09:40 - 10:50 | Room B109, IBS (기초과학연구원)
Program

9:40-10:05: Sang-il OUM, Obstructions for dense analogs of tree-depth
10:05-10:20: Kevin HENDREY, Structural and extremal results for twin-width
10:20-10:35: Rutger CAMPBELL, Down-sets in combinatorial posets
10:35-10:50: Linda COOK, Reuniting 𝜒-boundedness with polynomial 𝜒-boundedness

2023 Mini-Workshop on Discrete Geometry
2023-08-09 10:00 - 16:00 | Room B332, IBS (기초과학연구원)
2023 Mini-Workshop on Discrete Geometry will be held on August 9th at Room B332, Institute for Basic Science (IBS), Daejeon, Republic of Korea.
The workshop consists of three presentations on recent results and an open problem session.
Researchers who are highly interested in this field are welcome to attend.
Tentative schedule

10:00-10:50 Michael Dobbins (SUNY Binghamton): Colorful intersections, Tverberg partitions, and geometric transversals
11:00-11:30 Andreas Holmsen (KAIST): The topology of the complex of ordered partitions
11:30-13:30 Lunch and free discussion
13:30-14:10 Minki Kim김민기 (GIST): Some variants of the colorful Helly theorems
14:20-16:00 Open problem session
16:30-17:30 Discrete Math Seminar: R. Amzi Jeffs (Carnegie Mellon University)

Organizers

Andreas Holmsen (KAIST)
Jinha Kim김진하 (IBS Discrete Mathematics Group)
Minki Kim김민기 (GIST)
Sang-il Oum엄상일 (IBS Discrete Mathematics Group / KAIST)

Abstracts
Michael Dobbins (SUNY Binghamton): Colorful intersections, Tverberg partitions, and geometric transversals
Given three red convex sets and three blue convex sets in three-dimensional space, suppose every red set intersects every blue set. Montejano’s theorem says there is a line that intersects all the red sets or all the blue sets. This was generalized to k-transversals in $mathbb R^d$ by Montejano and Karasev using sophisticated algebraic and topological tools. Here we give further generalizations based on more accessible methods such as the test-map/configuration space scheme, Sarkaria’s tensor method, and discrete Morse theory.
Andreas Holmsen (KAIST): The topology of the complex of ordered partitions
The set of partitions of {1,…,n} into k nonempty ordered parts can be equipped with a natural cell-complex structure which we denote by P(n,k). Here we use discrete Morse theory to show that P(n,k) is homotopy equivalent to a wedge of (n-k)-dimensional spheres, where the number of spheres is given in terms of Stirling numbers of the second kind. Our result has applications related to geometric transversals and Tverberg partitions.
Minki Kim (GIST): Some variants of the colorful Helly theorems

Given a finite family $F$ of nonempty sets, the nerve of $F$ is the simplicial complex on $F$ whose simplices are precisely the intersecting subfamilies of $F$. The colorful Helly theorem, which generalizes Helly’s theorem, asserts the following: if $X$ is the nerve of the disjoint union of $d+1$ many finite families $F_1,ldots,F_{d+1}$ of convex sets in $mathbb{R}^d$ where each $F_i$ is not a simplex in $X$, then there is a colorful $(d+1)$-tuple that is not a simplex of $X$. It was shown by Kalai and Meshulam that the same statement holds for $d$-collapsible/Leray complexes. In this talk, I will explain the notion of $d$-collapsibility and $d$-Lerayness of simplicial complexes, and present recent results on variants of the colorful Helly theorem and applications. This is based on joint work with Alan Lew.

2023 Vertex-Minor Workshop
2023-10-15 - 2023-10-20 | SONO BELLE Jeju
This workshop aims to foster collaborative discussions and explore the various aspects of vertex-minors, including structural theory and their applications.
This event will be small-scale, allowing for focused talks and meaningful interactions among participants.
Website: https://indico.ibs.re.kr/event/596/

The 3rd East Asia Workshop on Extremal and Structural Graph Theory
2023-11-01 - 2023-11-05 | The Southern Beach Hotel & Resort Okinawa
The 3rd East Asia Workshop on Extremal and Structural Graph Theory is a workshop to bring active researchers in the field of extremal and structural graph theory, especially in the East Asia such as China, Japan, and Korea.
Website: http://tgt.ynu.ac.jp/2023EastAsia.html

IBS-DIMAG workshop on combinatorics and geometric measure theory
2024-07-15 - 2024-07-19 | Room B109, IBS (기초과학연구원)
Website: https://cgmt.dimag.kr/
Arrival Date: July 14, 2024 Sunday.
Departure Date: July 20, 2024 Saturday.
Organizers

Ben Lund (IBS Discrete Mathematics Group)
Doowon Koh (Chungbuk National University)
Sang-il Oum (IBS Discrete Mathematics Group / KAIST)

2024 Summer School on Combinatorics and Algorithms (2024 조합론 및 알고리즘 여름학교)
2024-07-22 - 2024-07-26 | Bldg. N1, KAIST
The 2024 Summer School on Combinatorics and Algorithms is a venue for students and early-career researchers to learn selected topics in theoretical computer science and discrete mathematics. It will be a great opportunity for young and aspiring researchers to study topics which are important but not covered during the lectures in the university classes. This summer, two lecture series, combinatorial optimization and grid minor theorem, will be given by two leading experts on the subjects. There will be exercise sessions where you form a team and solve challenging questions related to the lecture subjects.
Website: https://combialgo.dimag.kr/
Lecturers and Topics

Chien-Chung Huang (ENS Paris, France): Combinatorial Optimization

This lecture (12.5h) will cover essential topics in combinatorial optimization including: Berge’s theorem, Konig’s theorem, Egervary’s theorem, Karger’s min-cut algorithm and Gomory-Hu trees, Edmonds’ blossom algorithm for maximum matching, matroid 101, multi-commodity flow and k-coverage problems.

Sebastian Wiederrecht (DIMAG-IBS, Korea): From treewidth to grid minor theorem

This lecture (6h) will present the notion of tree decomposition, treewidth and graph minor, and introduce the grid minor theorem by Robertson and Seymour. Grid minor theory is deemed as one of the most important theory in modern graph theory and has many applications in algorithms design, data structure, logic, etc.

2024 Korean Student Combinatorics Workshop (KSCW2024, 2024 조합론 학생 워크샵)
2024-07-29 - 2024-08-02 | Gongju Hanok Village, Gongju
Venue
Gongju Hanok Vilage (공주한옥마을)
Organizers

Donggyu Kim (김동규), KAIST and IBS Discrete Mathematics Group
Seokbeom Kim (김석범), KAIST and IBS Discrete Mathematics Group
Seonghyuk Im (임성혁), KAIST and IBS Extremal Combinatorics and Probability Group
Hyunwoo Lee (이현우), KAIST and IBS Extremal Combinatorics and Probability Group

2024 Workshop on (Mostly) Matroids
2024-08-19 - 2024-08-23 | IBS Science Culture Center
The 2024 Workshop on (Mostly) Matroids will be held in-person at the Institute for Basic Science (IBS), Daejeon, South Korea, from August 19, 2024 to August 23, 2024. We expect that most people would arrive on Sunday, August 18 and leave on Saturday, August 24.
Our hope is that this workshop will continue the tradition of previous workshops held in Sittard (2008), Maastricht (2010,2012), Princeton (2014), Eindhoven(2016), Waterloo (2017), and Baton Rouge (2019). The focus will be on all aspects of matroid theory, including its connection to graph theory, algebraic geometry, and other areas of mathematics.

2024 Combinatorics Workshop (2024 조합론 학술대회)
2024-08-28 - 2024-08-30 | Chungbuk National University
Website: https://cw2024.combinatorics.kr/
Location
Chungbuk National University, Cheongju, Korea.
Advisory Committee

Committee of Discrete Mathematics, The Korean Mathematical Society (Chair: Sang-il Oum, IBS Discrete Mathematics Group / KAIST)

Sponsors

IBS Discrete Mathematics Group.
Korean Mathematical Society

IBS-DIMAG Workshop on Topology and Combinatorics
2024-11-11 11:00 - 17:30 | Room B332, IBS (기초과학연구원)
The IBS-DIMAG Workshop on Topology and Combinatorics will be held on November 11, 2024 at Room B332, Institute for Basic Science (IBS), Daejeon, South Korea.
Invited Speakers (tentative)

Karim Adiprasito (Jussieu Institute of Mathematics)
Minho Cho조민호 (IBS Extremal Combinatorics and Probability Group)
Niloufar Fuladi (INRIA Center of Université de Lorraine)
Minki Kim김민기 (GIST)
Dohyeon Lee이도현 (KAIST & IBS Discrete Mathematics Group)
Geunho Lim임근호 (Jussieu Institute of Mathematics)
Semin Yoo유세민 (IBS Discrete Mathematics Group)

Tentative Schedule

11:00-11:30 Karim Adiprasito, The Charney Davis conjecture and Boolean decompositions
12:00-14:00 Lunch Break
14:00-14:30 Niloufar Fuladi, Universal families of arcs and curves on surfaces
14:30-15:00 Semin Yoo유세민, The Charney-Davis conjecture and its related complexes (survey)
15:00-15:30 Geunho Lim임근호, Bounds on Cheeger-Gromov invariants and simplicial complexity of triangulated manifolds
15:30-16:00 Break
16:00-16:30 Minki Kim김민기, Some extensions of the colorful Helly theorem
16:30-17:00 Minho Cho조민호, Fractional Helly theorems via weak saturation
17:00-17:30 Dohyeon Lee이도현, Betti number of clique complex of H-free graphs (survey)
18:00-20:00 Banquet

Organizer

Semin Yoo유세민, IBS Discrete Mathematics Group

Abstracts
Karim Adiprasito, The Charney Davis conjecture and Boolean decompositions
I will present a novel approach to the Charney Davis conjecture by introducing anticommutative Lefschetz properties, and studying them on the Danzer complex of flag spheres.
Semin Yoo, The Charney-Davis conjecture and its related complexes (survey)
The Charney-Davis conjecture lies in the intersection between topology and combinatorics. The conjecture is a special case of the Hopf-Chern-Thurston conjecture for all nonpositively curved, piecewise Euclidean manifolds which are cellulated by regular Euclidean cubes. In 2001, Davis and Okun solved the conjecture for a 4-dimensional case, and some other partial results are also known. However, the conjecture is still open so far.
In this talk, I will describe five statements that solve the Charney-Davis conjecture and explain some complexes to achieve this goal.
Niloufar Fuladi, Universal families of arcs and curves on surfaces
In this talk I introduce a family of curves that realize all pants decomposition of a surface: a family of simple closed curves Γ on a surface realizes all types of pants decompositions if for any pants decomposition of the surface, there exists a homeomorphism sending it to a subset of the curves in Γ. The study of such universal families of curves is motivated by questions on graph embeddings, joint crossing numbers and finding an elusive center of moduli space. I will discuss the case of surfaces without punctures, where we establish an exponential upper bound and a superlinear lower bound on the minimum size of the family of curves with this universal property. I also talk about a similar concept of universality for triangulations of polygons, where we provide bounds which are tight up to logarithmic factors. In this talk, I will explain the background and context and no prior knowledge in topology or surfaces is needed.
This is joint work with Arnaud de Mesmay and Hugo Parlier.
Geunho Lim, Bounds on Cheeger-Gromov invariants and simplicial complexity of triangulated manifolds
Using L^2 cohomology, Cheeger and Gromov define the L^2 rho-invariant on manifolds with arbitrary fundamental groups, as a generalization of the Atiyah-Singer rho-invariant. There are many interesting applications in geometry, topology, and combinatorics. In this talk, we show linear bounds on the rho-invariants in terms of simplicial complexity of manifolds by using hyperbolization methods. As applications, we give new concrete examples in the complexity theory of high-dimensional (homotopy) lens spaces. This is a joint work with Shmuel Weinberger.
Minki Kim, Some extensions of the colorful Helly theorem
Given $k > d$ finite families of convex sets in $mathbb{R}^d$, if every colorful $(d+1)$-tuple is intersecting, then the union of $k-d$ color classes is intersecting. This is known as the colorful Helly theorem. Based on recent joint work with Alan Lew, I will present some extensions of the colorful Helly theorem and their applications.
Minho Cho, Fractional Helly theorems via weak saturation
Two celebrated extensions of the classical Helly’s theorem are the fractional Helly theorem and the colorful Helly theorem. Bulavka, Goodarzi, and Tancer recently established the optimal bound for the unified generalization of the fractional and the colorful Helly theorems using a colored extension of the exterior algebra. In this talk, we introduce a combinatorial reduction of both the fractional Helly theorem and its colorful version to a classical problem in extremal combinatorics known as weak saturation. No such results connecting the fractional Helly theorem and weak saturation are known in the long history of literature. These reductions, along with basic linear algebraic arguments for the reduced weak saturation problems, let us give new short proofs of the optimal bounds for both the fractional Helly theorem and its colorful version without using exterior algebra.
This is joint work with Debsoumya Chakraborti, Jinha Kim, and Minki Kim.
Dohyeon Lee, Betti number of clique complex of H-free graphs (survey)
The clique complex of a graph is a simplicial complex whose faces correspond to cliques of the given graph. In this talk, we investigate extremal properties of the Betti numbers of clique complexes. While general simplicial complexes with n vertices can have a total Betti number approximately $2^n$, Adamaszek showed that Betti number of clique complex is bounded by around $1.32^n$. Furthermore, if the underlying graph has an independence number at most two, the bound tightens to $1.25^n$. Adiprasito, Nevo, and Tancer established additional bounds on the total Betti number for clique complexes of (induced) H-free graphs for various graph H, along with constructions of graphs with large total Betti number. In another direction, Zhang and Wu demonstrated that for ternary graphs (whose with no induced cycles of length 3n), the Betti number of the independence complex (the clique complex of the complement of a graph) is at most one. Indeed, Jinha Kim showed that these independence complexes are either contractible or homotopy spheres.

IBS-DIMAG Winter School on Graph Minors, Week 1
2025-02-03 - 2025-02-05 | Room B109, IBS (기초과학연구원)

IBS-DIMAG Winter School on Graph Minors, Week 2
2025-02-10 - 2025-02-12 | Room B109, IBS (기초과학연구원)

IBS-DIMAG Winter School on Graph Minors, Week 3
2025-02-17 - 2025-02-19 | Room B109, IBS (기초과학연구원)

2025 Summer School on Combinatorics and Algorithms (2025 조합론 및 알고리즘 여름학교)
2025-07-14 14:00 - 2025-07-18 17:00 | POSTECH, Pohang, Korea
The 2025 Summer School on Combinatorics and Algorithms is a venue for students and early-career researchers to learn selected topics in theoretical computer science and discrete mathematics. It will be a great opportunity for young and aspiring researchers to study topics which are important but not covered during the lectures in the university classes.
Website: https://combialgo.dimag.kr/
Lecturers and Topics

Édouard Bonnet, LIP, CNRS.

Induced Subgraphs and Induced Minors of Graphs

Michał Pilipczuk, University of Warsaw.

Structural Theory of Sparse Graphs

Schedule

Start on 14 July 2025 Monday, 2 PM
End on 18 July 2025 Friday, 5 PM

2025 Combinatorics Workshop (2025 조합론 학술대회)
2025-08-18 - 2025-08-20 | IBS Science Culture Center
Website: https://cw2025.combinatorics.kr
Invited Speakers

Dongsu Kim (KAIST)
Eun Jung Kim (KAIST)
O-joung Kwon (Hanyang University)
Ae Ja Lee (Pennsylvania State University)
Zhicong Lin (Shandong University)

Organizing Committee

Sang-il Oum (엄상일), IBS Discrete Mathematics Group
Jang Soo Kim (김장수), Sungkyunkwan University
Seunghyun Seo (서승현), Kangwon National University

2025 Korean Student Combinatorics Workshop (KSCW2025: 2025 조합론 학생 워크샵)
2025-08-20 - 2025-08-24 | The K-Hotel Gyeongju
Venue
The K-Hotel Gyeongju
Website
https://indico.ibs.re.kr/e/kscw2025
Organizers

Seokbeom Kim (김석범), KAIST and IBS Discrete Mathematics Group
Hyunwoo Lee (이현우), KAIST and IBS Extremal Combinatorics and Probability Group
Jaehyeon Seo (서재현), Yonsei University
Kyungjin Cho (조경진), POSTECH

5th East Asia Workshop on Extremal and Structural Graph Theory
2025-11-27 - 2025-11-30 | Seoul, Korea
The 5th East Asia Workshop on Extremal and Structural Graph Theory is a workshop to bring active researchers in the field of extremal and structural graph theory, especially in the East Asia such as China, Japan, and Korea.

Date
November 27, 2025 Thursday (Arrival Day) — November 30, 2025 Sunday (Departure Day)
Venue
Fraser Place Namdaemun, Seoul
Program Book
Invited Speakers

Shinya Fujita (Yokohama City University)
Jie Han (Beijing Institute of Technology)
Tony Huynh (IBS Discrete Mathematics Group)
Jaehoon Kim (KAIST)
O-joung Kwon (Hanyang University / IBS Discrete Mathematics Group)
Hong Liu (IBS Extremal Combinatorics and Probability Group)
Jie Ma (University of Science and Technology of China / Tsinghua University)
Shun-ichi Maezawa (Nihon University)
Boram Park (Seoul National University)
Shohei Satake (Kumamoto University)
Tuan Tran (University of Science and Technology of China)
Shoichi Tsuchiya (Senshu University)
Xuding Zhu (Zhejiang Normal University)

Organizers
Seog-Jin Kim, Sang-il Oum, Kenta Ozeki, Hehui Wu
Registration
Invitation Only. https://indico.ibs.re.kr/event/1041/
There is no registration fee and one dinner (banquet) will be provided.
History

4th East Asia Workshop on Extremal and Structural Graph Theory

Mar. 27 – Mar. 31, 2025.
School of Mathematics, Sun-Yet Sen University, Guangzhou, China
Organizers: Ping Hu, Seog-Jin Kim, Kenta Ozeki, Hehui Wu.

3rd East Asia Workshop on Extremal and Structural Graph Theory

Nov. 1- Nov. 5, 2023.
The Southern Beach Hotel & Resort, Okinawa, Japan
Sponsored by the IBS Discrete Mathematics Group, Korea.
Organizers: Seog-Jin Kim, Sang-il Oum, Kenta Ozeki, Hehui Wu.

2nd East Asia Workshop on Extremal and Structural Graph Theory

Oct. 31-Nov. 4, 2019.
Held at UTOP UBLESS Hotel, Jeju, Korea
Sponsored by the IBS Discrete Mathematics Group, Korea.
Organizers: Seog-Jin Kim, Sang-il Oum, Kenta Ozeki, Hehui Wu.

1st East Asia Workshop on Extremal and Structural Graph Theory

Nov. 30-Dec. 2, 2018.
Held and sponsored by the Shanghai Center for Mathematical Sciences in China, under the name 2018 SCMS Workshop on Extremal and Structural Graph Theory.
Organizers: Ping Hu, Seog-Jin Kim, Kenta Ozeki, Hehui Wu.

Thursday
November 27, 2025

Time
Speaker
Affiliation
Title

16:00–18:00

Registration & Discussions

Friday
November 28, 2025

Time
Speaker
Affiliation
Title

09:20–10:00
Jaehoon Kim
KAIST
Hamilton cycles in pseudorandom graphs: Dirac’s theorem and approximate decompositions

10:00–10:30

Coffee Break

10:30–11:10
Jie Ma
University of Science and Technology of China / Tsinghua University
An exponential improvement for Ramsey lower bounds

11:20–12:00
Shinya Fujita
Yokohama City University
Connectivity keeping paths containing prescribed vertices in highly connected triangle-free graphs

12:00–14:00

Lunch Break

14:00–14:40
Shun-ichi Maezawa
Nihon University
Tree versus tree of preorder induced by rainbow forbidden subgraphs

14:50–15:30
Tony Huynh
IBS Discrete Mathematics Group
Rainbow triangles and the Erdős–Hajnal problem in projective geometries

15:30–15:50

Coffee Break

16:30–17:30

Problem Session

Saturday
November 29, 2025

Time
Speaker
Affiliation
Title

09:20–10:00
Xuding Zhu
Zhejiang Normal University
TBA

10:00–10:30

Coffee Break

10:30–11:10
Hong Liu
IBS Extremal Combinatorics and Probability Group
Chromatic, homomorphism, blowup thresholds and beyond

11:20–12:00
Shohei Satake
Kumamoto University
TBA

12:00–14:00

Lunch Break

14:00–14:40
Shoichi Tsuchiya
Senshu University
On the number of contractible edges in plane triangulations

14:50–15:30
Tuan Tran
University of Science and Technology of China
Littlewood-Offord bounds on the symmetric groups and applications

15:30–15:50

Coffee Break

15:50–16:30
O-joung Kwon
Hanyang University / IBS Discrete Mathematics Group
A coarse Erdős–Pósa theorem

16:30–17:30

Problem Session

18:30–21:00

Banquet

Sunday
November 30, 2025

Time
Speaker
Affiliation
Title

10:00–10:40
Jie Han
Beijing Institute of Technology
Perturbation of dense graphs

10:40–10:50

Break

10:50–11:30
Boram Park
Seoul National University
Graphs avoiding cycles of length 0 modulo 4

11:30–12:00

Closing

2026 Workshop on Topological Combinatorics
2026-06-28 - 2026-07-11 | GIST
The 2026 Workshop on Topological Combinatorics will be held from June 28 to July 11, 2026 at Gwangju Institute of Science and Technology (GIST), located in Gwangju in the southwest of Republic of Korea.
The workshop aims to bring together researchers interested in applications of topology to combinatorics and related areas. This will be the fifth workshop in a series initiated by Ron Aharoni (August 2018 in Shantou, July 2019 in Prague, July 2020 on Zoom, and June 2024 in Paris).
The first week (June 28 – July 04) will be reserved for presentations, while the following days (July 05 – July 11) will be for discussion and collaborations.
The campus offers a variety of amenities, including a guesthouse that can accommodate approximately 20 guests.
In addition, various lodging options are available within a 15–20 minute walking distance.
We are planning to provide accommodation for all invited participants, and we are also considering offering partial travel support for those with limited funding.

Website: https://sites.google.com/view/2026topocomb

2026 Korean Student Combinatorics Workshop
2026-07-27 - 2026-07-31 | Gongju Hanok Village, Gongju
Website: https://kscw.combinatorics.kr/

2026 Summer School on Combinatorics and Algorithms (2026 조합론 및 알고리즘 여름학교)
2026-08-10 - 2026-08-14 | Bldg. E11, KAIST
The 2026 Summer School on Combinatorics and Algorithms is a venue for students and early-career researchers to learn selected topics in theoretical computer science and discrete mathematics. It will be a great opportunity for young and aspiring researchers to study topics which are important but not covered during the lectures in the university classes.
Website: https://combialgo.dimag.kr/2026/
Lecturers and Topics

Daniel Dadush, CWI, Amsterdam

Algorithms & Geometry of Linear Programming

Magnus Wahlström, Royal Holloway, University of London

Matroids, delta-matroids, and applications

Schedule

Start on 10 August 2026 Monday, 2 PM
End on 14 August 2025 Friday, 5 PM

2026 Combinatorics Workshop (2026 조합론 학술대회)
2026-10-20 - 2026-10-22 | Konjiam Resort, EW Village, B2, Meeting Room OPUS2
Combinatorics Workshop (조합론 학술대회) is an annual conference for researchers in combinatorics and related areas in Korea. It was started in 2004 by the Yonsei University BK21 Research Group. Since 2013, this workshop has been advised by the committee of discrete mathematics of the Korean Mathematical Society.
Website: https://cw2026.combinatorics.kr/en/
Venue
Konjiam Resort, EW Village, B2, Meeting Room OPUS2
(278, Docheogwit-Ro, Docheok-Myeon, Gwangju-Si, Gyeonggi-Do, Korea)

Travel Instructions

Dates
October 20 to 22, 2026
Plenary Speaker
Alexander V. Kostochka (UIUC)
Invited Speakers

Cheolwon Heo (SUNY Korea)
Tony Huynh (IBS DIMAG)
Dabeen Lee (Seoul National University)
Jongbaek Song (Pusan National University)

Contributed Talks
Each contributed talk will be about 20 minutes, including questions. Please note that we may stop accepting contributed talk applications before the deadline if all available slots are filled.
If you are interested in giving a contributed talk at the workshop, please submit an abstract by August 31, 2026.
To apply for a contributed talk, go to Call for Abstracts on Indico and click “Submit new abstract.” You may need to create an IBS Indico account.
Registration
Registration link
The registration deadline is August 31, 2026.
Organizing Committee

Ilkyoo Choi (최일규), Hankuk University of Foreign Studies, IBS Discrete Mathematics Group, KIAS
Sang-il Oum (엄상일), IBS Discrete Mathematics Group
Boram Park (박보람), Seoul National University

Advisory Committee
Committee of Discrete Mathematics, The Korean Mathematical Society (Chair: Sang-il Oum)
Sponsors

IBS Discrete Mathematics Group
Korean Mathematical Society
Seoul National University
Hankuk University of Foreign Studies
