## Jaeseong Oh (오재성) gave a talk on the condition of ribbon graphs sharing the same delta-matroid at the Discrete Math Seminar

On November 3, 2020, Jaeseong Oh (오재성) from Seoul National University presented his work with Iain Moffatt on the characterization of ribbon graphs having the same delta-matroid. The title of his talk is “A 2-isomorphism theorem for delta-matroids“.

## Jaeseong Oh (오재성), A 2-isomorphism theorem for delta-matroids

Whitney’s 2-Isomorphism Theorem characterises when two graphs have isomorphic cycle matroids. In this talk, we present an analogue of this theorem for graphs embedded in surfaces by characterising when two graphs in surface have isomorphic delta-matroids. This is based on the joint work with Iain Moffatt.

## 2020 Combinatorics Workshop (2020 조합론 학술대회) was held on August 24 online

On August 24, Monday, the 2020 Combinatorics Workshop (2020 조합론 학술대회) was held online due to the COVID-19 pandemic. This local workshop series began in 2004 and has been continued to be one of the biggest annual gathering of people in combinatorics located in Korea. Due to the COVID-19 pandemic, it has been reduced to a one-day online conference on Zoom. It was hosted by Kyung Hee University and IBS Discrete Mathematics Group.

The workshop website: https://cw2020.combinatorics.kr

## There were 5 invited speakers.

• Sejeong Bang (방세정), Yeungnam University, Geometric distance-regular graphs
• Ringi Kim (김린기), KAIST, Decomposing planar graphs into graphs with degree restrictions
• Sangwook Kim (김상욱), Chonnam National University, Combinatorics of lattice path matroid polytopes
• Jinyoung Park (박진영), Institute for Advanced Study, Tuza’s Conjecture for random graphs
• Jongyook Park (박종육), Kyungpook National University, On distance-regular graphs with induced subgraphs $K_{r,t}$

## There were 4 contributed talks.

• Byung-Hak Hwang (황병학), Seoul National University, Acyclic orientation polynomials
• Jaeseong Oh (오재성), Seoul National University, On linearization coefficients of q-Laguerre polynomials
• Jun Seok Oh (오준석), Incheon National University, An inverse Erdős-Ginzburg-Ziv theorem for finite groups
• Tuan Tran, IBS Discrete Mathematics Group, The singularity of random combinatorial matrices

## 2020 Combinatorics Workshop

Combinatorics Workshop (조합론 학술대회) is the biggest annual conference in combinatorics in Korea. It was firstly held in 2004 by the Yonsei University BK21 Research Group. It has been advised by the committee of discrete mathematics of the Korean Mathematical Society since 2013. The aim of this workshop is to bring active researchers with different backgrounds to discuss recent and prospective advances in combinatorics and related areas.

Originally, we planned an offline workshop. However, COVID 19 is more spreading and many participants are worried about attending an offline conference. So the schedule and venue are changed as an online workshop with Zoom. I hope that all participants generously understand this sudden change.

# Contributed speakers

• Byung-Hak Hwang (황병학), Seoul National University
• Jaeseong Oh (오재성), Seoul National University
• Jun Seok Oh (오준석), Incheon National University
• Tuan Tran, Institute for Basic Science (IBS)