I am one of the members organizing Incheon Combinatorics (offline) Seminar. We organize meetings in Thursday (Incheon National University, Inha University) or Friday (SUNY Korea) for this spring semester. We are happy to invite you to give a talk. Please e-mail me if you are interested in.

DATE : 12th, May, 2020 (10am-11am)

TITLE : Vertex-minor-closed classes are chi-bounded (operated by zoom)

SPEAKER : James Davis (University of Waterloo)

ABSTRACT :

We prove a conjecture of Geelen that vertex-minor-closed classes of graphs are chi-bounded. We will define vertex-minors and chi-boundedness in the talk.

DATE : 30th, Apr, 2019 (5-6pm).

TITLE: Structural graph theory, vertex minors, and circle graphs

SPEAKER : Rose McCarty (University of Waterloo)

ABSTRACT : TBA

DATE : 9th, Apr, 2019 (5-6pm).

TITLE: Counting self-conjugate simultaneous core partitions

SPEAKER : Jisun Huh

ABSTRACT : In this talk, we consider counting self-conjugate simultaneous core partitions based on my recent works with Hyunsoo Cho and Jaebum Sohn:

– A bijection between ordinary partitions and self-conjugate partitions with same disparity

-Counting self-conjugate (s,s+1,s+2)-core partitions

For each box in the Young diagram of a partition, we define its hook length by counting the number of boxes directly to its right or below, including the box itself. For a positive integer t, a partition is called a t-core if none of its hook lengths are multiples of t. Since the work [1] of Anderson, the topic counting simultaneous cores has received growing attention. By using several methods, we count the number of simultaneous core partitions with some restrictions and found closed formulae for these numbers.

[1] Jaclyn Anderson. Partitions which are simultaneously $t_1$- and $t_2$-core. Discrete Math., 248(1-3):237-243,2002.

DATE : 11th, Oct, 2018 (10am-3pm)

There will be a one-day graph theory workshop at INU. Detailed information can be found at http://ojkwon.com/seminar/inugraph/.

DATE : 5th, Apr, 2018 (4-5pm).

TITLE: Sharp bound on the number of maximal sum-free subsets of integers

SPEAKER : Hong Liu

DATE : 19th, Apr, 2018 (4:20-5:10pm).

TITLE: Forbidding induced even cycles in a graph: typical structure and counting

SPEAKER : Jaehoon Kim

ABSTRACT : We determine, for all k≥6, the typical structure of graphs that do not contain an induced 2k-cycle. This verifies a conjecture of Balogh and Butterfield. Surprisingly, the typical structure of such graphs is richer than that encountered in related results. The approach we take also yields an approximate result on the typical structure of graphs without an induced 8-cycle or without an induced 10-cycle.

DATE : 12th, June, 2018 (4:00-4:50pm).

TITLE: Helly type theorems in combinatorics

SPEAKER : Minki Kim

ABSTRACT : Helly’s theorem is one of the most well-known and fundamental result about intersection patterns of convex in Euclidean spaces. It asserts that for a finite family $\mathcal{F}$ of convex sets in $\mathbb{R}^d$, if every $d+1$ or fewer members of $\mathcal{F}$ have a point in common, then all members of the family $\mathcal{F}$ have a point in common. There are a remarkable number of variants and applications of Helly’s theorem, and these results are called Helly type theorems. In this talk, I will give a brief overview on classical Helly type theorems, and introduce some recent generalizations of Helly’s theorem.