# Upcoming Events

## April 2019

### Speaker

Circle graphs are the intersection graphs of chords on a circle; vertices correspond to chords, and two vertices are adjacent if their chords intersect. We prove that every circle graph with clique number k has chromatic number at most $4k^2$. Joint with James Davies.

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## May 2019

### Speaker

Let $\mathbb N$ be the set of natural numbers. A set $A\subset \mathbb N$ is called a Sidon set if the sums $a_1+a_2$, with $a_1,a_2\in S$ and $a_1\leq a_2$, are distinct, or equivalently, if \ for every $x,y,z,w\in S$ with $x<y\leq z<w$. We define strong Sidon sets as follows: For a constant $\alpha$ with $0\leq \alpha<1$, a set $S\subset \mathbb N$ is called an $\alpha$-strong Sidon set if \ for every $x,y,z,w\in S$ with $x<y\leq z<w$. The motivation of strong Sidon…

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### Speaker

An equitable tree-$k$-coloring of a graph is a vertex coloring using $k$ distinct colors such that every color class (i.e, the set of vertices in a common color) induces a forest and the sizes of any two color classes differ by at most one. The minimum integer $k$ such that a graph $G$ is equitably tree-$k$-colorable is the equitable vertex arboricity of $G$, denoted by $va_{eq}(G)$. A graph that is equitably tree-$k$-colorable may admits no equitable tree-$k'$-coloring for some $k'>k$.…

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### Speaker

A $b$-coloring of a graph $G$ is a proper coloring of its vertices such that each color class contains a vertex that has at least one neighbor in all the other color classes. The $b$-Coloring problem asks whether a graph $G$ has a $b$-coloring with $k$ colors. The $b$-chromatic number of a graph $G$, denoted by $\chi_b(G)$, is the maximum number $k$ such that $G$ admits a $b$-coloring with $k$ colors. We consider the complexity of the $b$-Coloring problem, whenever…

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## July 2019

### 2019 IBS Summer Research Program on Algorithms and Complexity in Discrete Structures

An invitation-only summer research program will be held in the summer of 2019. There will be 10-20 participants to work together at DIMAG. More details will be posted later. Registered Participants Nick Brettell (Eindhoven University of Technology) Yixin Cao (Hong Kong Polytechnic University) Archontia Giannopoulou (National and Kapodistrian University of Athens) Mamadou M. Kante (University Clermont Auvergne) Michael Dobbins (Binghamton University) Aboulker Pierre (ENS)

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기초과학연구원 수리및계산과학연구단 이산수학그룹
대전 유성구 엑스포로 55 (우) 34126
Discrete Mathematics Group (DIMAG)
Pioneer Research Center for Mathematical and Computational Sciences
Institute for Basic Science (IBS)
55 Expo-ro Yuseong-gu Daejeon 34126 South Korea
E-mail: dimag@ibs.re.kr