On April 1, 2022, Hong Liu from the University of Warwick is appointed as the Chief Investigator to lead a new group, the IBS Extremal Combinatorics and Probability Group (ECOPRO), in the Center for Mathematical and Computational Sciences. To enhance our collaboration, the IBS Discrete Mathematics Group will move to the 3rd floor of the theory building on April 19-21 to share the space with the Extremal Combinatorics and Probability Group.

## “2021 Combinatorics Workshop” was held from December 20 to December 22, 2021 at Yangpyeong

The 2021 Combinatorics Workshop (2021 조합론 학술대회) was held from December 20, 2021 to December 22, 2021 at the Bloomvista, Yangpyeong. There were 5 invited talks and 12 contributed talks.

### Invited Speakers

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

### Speakers of the contributed talks

- Jungho Ahn, KAIST / IBS DIMAG
- Jin-Hwan Cho, NIMS
- Linda Cook, IBS DIMAG
- Cheolwon Heo, Sungkyunkwan University
- Seonghyuk Im, KAIST
- Hyobin Kim, Kyungpook National University
- Minki Kim, IBS DIMAG
- Hyemin Kwon, Ajou University
- Hyunwoo Lee, KAIST
- Sang June Lee, Kyung Hee University
- Jaehyeon Seo, KAIST
- Semin Yoo, KIAS

### Organizing Committee

- Jeong-Ok Choi, GIST
- Sang-il Oum, IBS DIMAG / KAIST
- Heesung Shin, Inha University

### Participants (50 people, all of whom are fully vaccinated against COVID-19)

- Jungho Ahn,
, KAIST / IBS DIMAG**speaker** - Sejeong Bang, session chair, Yeungnam University
- Rutger Campbell, IBS DIMAG
- Debsoumya Chakraborti, IBS DIMAG
- Eun-Kyung Cho, Hankuk University of Foreign Studies
- Hyunsoo Cho, Ewha Womans University
- Jin-Hwan Cho,
, NIMS**speaker** - Jeong-Ok Choi,
/session chair, GIST**organizer** - Linda Cook,
, IBS DIMAG**speaker** - Taehyun Eom, KAIST
- Cheolwon Heo,
, Sungkyunkwan University**speaker** - Seonghyuk Im,
, KAIST**speaker** - Jihyeug Jang, Sungkyunkwan University
- Dosang Joe, NIMS
- Donggyu Kim, KAIST / IBS DIMAG
- Donghyun Kim, Sungkyunkwan University
- Dongsu Kim,
, KAIST**invited speaker** - Hyobin Kim,
, Kyungpook National University**speaker** - Jaehoon Kim, KAIST
- Jang Soo Kim, Sungkyunkwan University
- Jinha Kim, IBS DIMAG
- Minki Kim,
, IBS DIMAG**speaker** - Seog-Jin Kim, session chair, Konkuk University
- Doowon Koh, Chungbuk National University
- Hyemin Kwon,
, Ajou University**speaker** - O-joung Kwon, Incheon National University / IBS DIMAG
- Dabeen Lee, IBS DIMAG
- Duksang Lee, KAIST / IBS DIMAG
- Hyunwoo Lee,
, KAIST**speaker** - Joonkyung Lee,
, Hanyang University**invited speaker** - Sang June Lee,
, Kyung Hee University**speaker** - Seung Jin Lee, Seoul National University
- Hong Liu,
, University of Warwick, UK**invited speaker** - Ben Lund, IBS DIMAG
- Suil O,
, SUNY Korea**invited speaker** - Jaeseong Oh, KIAS
- Sang-il Oum,
IBS DIMAG / KAIST**organizer**/session chair, - Jae Hyun Park, Kyung Hee University
- Seonjeong Park,
**invited**, Jeonju University**speaker** - Jaehyeon Seo,
, KAIST**speaker** - Seunghyun Seo, session chair, Kangwon National University
- Heesung Shin,
/session chair, Inha University**organizer** - Mark Siggers, Kyungpook National University
- Jaebum Sohn, Yonsei University
- Minho Song, Sungkyunkwan University
- U-keun Song, Sungkyunkwan University
- Jeong Hyun Sung, Seoul National University
- Tuan Tran, IBS DIMAG
- Sounggun Wee, KAIST / IBS DIMAG
- Semin Yoo,
, KIAS**speaker**

### Host and Sponsors

## Hong Liu is moving to IBS as a Chief Investigator to start the IBS Extremal Combinatorics and Probability Group (ECOPRO) on April 2022 and is hiring up to 5 postdocs in all fields of combinatorics with emphasis on extremal and probabilistic combinatorics, graph theory, Ramsey theory, combinatorial number theory and discrete geometry

We are very excited to learn that Prof. Hong Liu from University of Warwick, UK will move to the Institute for Basic Science (IBS) as a Chief Investigator (CI) to lead a new group called the Extremal Combinatorics and Probability Group (ECOPRO) on April 2022. This new group will be also located in the IBS headquarter and is expected to work closely with the IBS Discrete Mathematics Group (DIMAG). Both DIMAG and ECOPRO belong to the IBS Center for Mathematical and Computational Sciences together with the Data Science Group and the Biomedical Mathematics Group and we share the staff members.

The website was made recently. https://www.ibs.re.kr/ecopro/

Yesterday, the IBS Extremal Combinatorics and Probability Group (ECOPRO) posted the hiring announcement for up to 5 postdocs. Here are a few paragraphs from the announcement.

The Extremal Combinatorics and Probability Group (ECOPRO) at the Institute for Basic Science (IBS) in Daejeon, South Korea invites applications for 5 postdoctoral research fellowship positions. ECOPRO is a new research group that will be officially launched in April 1, 2022 at IBS, led by Prof. Hong Liu. We welcome highly motivated postdoc researchers with outstanding research potential in all fields of combinatorics with emphasis on extremal and probabilistic combinatorics, graph theory, Ramsey theory, combinatorial number theory and discrete geometry. This appointment is for 2 years with possible 1 year extension contingent upon the outstanding performance of the researcher. The starting salary is no less than 57,000,000 KRW (about 48,400 USD or 42,800 EUR). The appointment starting date is flexible: between April 1 and Oct 1, 2022. This is a purely research position and will have no teaching duties.

A complete application packet should include

- Curriculum vitae including a publication list (PDF format)
- Research statement (PDF format)
- Up to 3 best papers or preprints
- Consent to Collection and Use of Personal Information (Please convert to a PDF file)
- Two or three recommendation letters.

For full consideration, applicants should email items 1, 2, 3, and 4 and arrange their recommendation letters emailed to ecopro@ibs.re.kr by **January 14, 2022**.

Recommendations letters forwarded by an applicant will not be considered.

## Hong Liu gave a talk on the extremal problem of finding nested cycles with no geometric crossing at the Discrete Math Seminar

On March 22, 2021 at the Discrete Math Seminar, Hong Liu (刘鸿) from the University of Warwick gave a talk on the extremal problem of having nested cycles with no geometric crossing by using the sublinear expanders. The title of his talk was “Nested cycles with no geometric crossing“.

## Hong Liu presented his result with R. Montgomery on the resolution the odd cycle problem of Erdős and Hajnal at the Discrete Math Seminar

On December 8, 2020, Hong Liu from University of Warwick presented a talk on his recent work with Richard Montgomery, answering the odd cycle problem of Erdős and Hajnal (1981). The title of his talk is “A solution to Erdős and Hajnal’s odd cycle problem“.

## Hong Liu gave a talk describing approximate structures of an n-vertex m-edge graph minimizing the number of cliques of size k at the Discrete Math Seminar

On May 26, 2020, Hong Liu from University of Warwick presented a talk on his recent work describing approximate structures of an n-vertex m-edge graph minimizing the number of cliques of size k. The title of his talk was “Asymptotic Structure for the Clique Density Theorem”.

## Hong Liu gave a talk on the conjecture of Mader about the topological minors in C4-free graphs at the discrete math seminar

On December 12, 2019, Hong Liu from University of Warwick gave a talk on the resolution of the conjecture of Mader on the existence of a complete topological minor under the condition of average degree for C4-free graphs at the discrete math seminar held at KAIST. The title of his talk was “A proof of Mader’s conjecture on large clique subdivisions in $C_4$-free graphs“.

## “2019-2 IBS One-Day Conference on Extremal Graph Theory” was held on August 12, 2019.

The 2019-2 IBS One-Day Conference on Extremal Graph Theory was held on August 12, 2019 at the IBS Discrete Mathematics Group. There were four talks. Here is a list of talks.

- Jaehoon Kim (김재훈), KAIST:
*Tree decompositions of graphs without large bipartite holes* - Hong Liu (刘鸿), University of Warwick:
*Recent advance in Ramsey-Turán theory* - Abhishek Methuku, IBS Discrete Mathematics Group:
*Bipartite Turán problems for ordered graphs* - Péter Pál Pach, Budapest University of Technology and Economics:
*On some applications of graph theory to number theoretic problems*

## Hong Liu gave the second discrete math seminar talk at IBS DIMAG

Hong Liu from University of Warwick, UK gave the discrete math seminar talk at DIMAG on his recent work “polynomial Schur’s theorem” on December 13, 2018.