The “Round the World Relay in Combinatorics” was held from 11 am KST of June 8 to 9 am KST of June 9. O-joung Kwon (권오정) from the Incheon National University and the IBS Discrete Mathematics Group gave a talk at the Discrete Math Seminar organized as a part of the “Round the World Relay in Combinatorics” at 3 pm KST. His talk was about classes of intersection digraphs and their bi-min-width. The title of his talk was “Classes of intersection digraphs with good algorithmic properties“.

## Adam Zsolt Wagner gave an online talk on disproving graph theory conjectures by using reinforcement learning at the Virtual Discrete Math Colloquium

On June 2, 2021, Adam Zsolt Wagner from the Tel Aviv University gave an online talk at the Virtual Discrete Math Colloquium on disproving graph theory conjectures by using reinforcement learning. The title of the talk was “Constructions in combinatorics via neural networks“.

## “Round the World Relay in Combinatorics” will be held on June 8 Tuesday, 2021 from 2:00 UTC (=11 am in Korea) to 24:00 UTC (=9 am next day in Korea)

IBS DIMAG is very happy to join the first international effort to have a full day of online talks in combinatorics. It’ll be on Zoom.

meeting id: 875 9395 3555 (relay)

Website: http://people.maths.ox.ac.uk/scott/relay.htm

## June 8 Tuesday, 2021

- 2:00 UTC, 11:00 KST Melbourne (Australia) Monash University
**David Wood**(Monash University),*Universality in Minor-Closed Graph Classes*

- 3:00 UTC, 12:00 KST Shanghai (China) Shanghai Center for Mathematical Sciences
**Baogang Xu**(Nanjing Normal University, China),*On coloring of graphs of girth 2l+1 without longer odd holes*

- 4:00 UTC, 13:00 KST Auckland (New Zealand) The University of Auckland
**Jeroen Schillewaert**(University of Auckland),*Constructing highly regular expanders from hyperbolic Coxeter groups*

- 5:00 UTC, 14:00 KST Sydney (Australia) Combinatorial Mathematics Society of Australasia
**Gordon Royle**(University of Western Australia (UWA)),*Real chromatic roots of planar graphs*

- 6:00 UTC, 15:00 KST Daejeon (Korea) IBS Discrete Mathematics Group
**O-joung Kwon**(Incheon National University and IBS Discrete Mathematics Group),*Classes of intersection digraphs with good algorithmic properties*

- 7:00 UTC, 16:00 KST Krakow (Poland) Jagiellonian University
**Bartosz Walczak**(Jagiellonian),*Coloring polygon visibility graphs and their generalizations*

- 8:00 UTC, 17:00 KST Glasgow (UK) University of Glasgow
**Heng Guo**(University of Edinburgh),*A Markov chain approach towards the sampling Lovász local lemma*

- 9:00 UTC, 18:00 KST London (UK) London School of Economics
**Annika Heckel**(LMU),*How does the chromatic number of a random graph vary?*

- 10:00 UTC, 19:00 KST Moscow (Russia) Moscow Institute of Physics and Technology
**Noga Alon**(Princeton and Tel Aviv),*Splitting random necklaces*

- 11:00 UTC, 20:00 KST Budapest (Hungary) Hungarian Academy of Sciences + Eötvös Loránd University
**László Lovász**(Eötvös University, Budapest),*Orthogonal representations and graph limits*

- 12:00 UTC, 21:00 KST Bordeaux (France) LaBRI
**Carla Groenland**(Utrecht University), Universal Graphs and Labelling Schemes

- 13:00 UTC, 22:00 KST New York (USA) City University of New York + Montclair State University + Hofstra University
**Deepak Bal**(Montclair State University),*Size Ramsey numbers of paths and cycles*

- 14:00 UTC, 23:00 KST Prague (Czech) Czech Academy of Sciences + Czech Technical University + London School of Economics
**Dhruv Mubayi**(University of Illinois at Chicago),*The feasible region of hypergraphs*

- 15:00 UTC, 00:00 KST Brno (Czech) Masaryk University
**James Davies**(University of Waterloo),*Colouring circle graphs and their generalisations*

- 16:00 UTC, 01:00 KST Oxford (UK) University of Oxford
**Jacob Fox**(Stanford University),*Removal lemmas*

- 17:00 UTC, 02:00 KST Columbus (USA) Ohio State University
**Allan Sly**(Princeton University),*Spread of infections in random walkers*

- 18:00 UTC, 03:00 KST Rio (Brazil) Instituto de Matemática Pura e Aplicada
**Marcelo Campos**(IMPA),*The singularity probability of a random symmetric matrix is exponentially small*

- 19:00 UTC, 04:00 KST Atlanta (USA) Georgia Institute of Technology
**Jim Geelen**(University of Waterloo),*Homomorphisms and colouring for graphs and binary matroids*

- 20:00 UTC, 05:00 KST Santiago (Chile) Universidad de Chile
**David Conlon**(Caltech),*Random multilinear maps and the Erdős box problem*

- 21:00 UTC, 06:00 KST Burnaby (Canada) Simon Fraser University
**Fan Chung**(UCSD),*Trees and forests in Green’s functions of a graph*

- 22:00 UTC, 07:00 KST Victoria (Canada) University of Victoria
**Andrew Suk**(UCSD),*Turán-type problems for point-line incidences*

- 23:00 UTC, 08:00 KST Fairbanks (USA) University of Alaska
**Ron Gould**(Emory),*Chorded cycles*

## Doowon Koh (고두원) gave a talk on a variation of the Erdős–Falconer distinct distance problem over finite fields at the Discrete Math Seminar

On June 1, 2021, Doowon Koh (고두원) from Chungbuk National University gave a talk on a variation of the Erdős–Falconer distinct distance problem over finite fields at the Discrete Math Seminar. The title of the talk was “Mattila-Sjölin type functions: A finite field model“.

## Dimitrios M. Thilikos gave an online talk on bounding the size of obstructions for minor-closed classes of graphs at the Virtual Discrete Math Colloquium

On May 26, 2021, Dimitrios M. Thilikos from LIRMM, CNRS gave an online talk at the Virtual Discrete Math Colloquium about an upper bound of the size of obstructions for minor-closed classes of graphs at the Virtual Discrete Math Colloquium. The title of the talk was “Bounding Obstructions sets: the cases of apices of minor closed classes“.

## Ben Lund gave a talk on the existence of a limit shape for lattice zonotopes at the Discrete Math Seminar

On May 25, 2021, Ben Lund from the IBS Discrete Mathematics Group gave a talk at the Discrete Math Seminar on the existence of a limit shape for lattice zonotopes in all dimensions and other relevant results. The title of his talk was “Limit shape of lattice Zonotopes”.

## Benjamin Bumpus gave an online talk introducing directed branch-width for directed graphs at the Virtual Discrete Math Colloquium

On May 21, 2021, Benjamin Bumpus from the University of Glasgow gave an online talk at the Virtual Discrete Math Colloquium about the directed branch-width for directed graphs. The title of his talk was “Directed branch-width: A directed analogue of tree-width“.

## Pascal Gollin gave a talk on extending a vertex-flame to a large vertex-flame in a countable digraph at the Discrete Math Seminar

On May 18, 2021, Pascal Gollin from the IBS Discrete Mathematics Group gave a talk at the Discrete Math Seminar on the existence of a large flame extending a given vertex-flame in a countable digraph. The title of his talk was “Enlarging vertex-flames in countable digraphs“.

## Johannes Carmesin gave an online talk on locally planar embeddability of graphs on a surface at the Virtual Discrete Math Colloquium

On May 12, 2021, Johannes Carmesin from the University of Birmingham gave an online talk at the Virtual Discrete Math Colloquium on the analogue of Whitney’s theorem for the locally planar embedding of graphs on a surface. The title of his talk was “A Whitney type theorem for surfaces: characterising graphs with locally planar embeddings“.

## Mark Siggers gave a talk on the complexity of the list switch homomorphism problem for signed graphs at the Discrete Math Seminar

On May 11, 2021, Mark Siggers from the Kyungpook National University gave a talk at the Discrete Math Seminar about the complexity of deciding whether there is a list homomorphism from a signed graph G to another signed graph switching equivalent to H. The title of his talk was “The list switch homomorphism problem for signed graphs“.