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PRODID:-//Discrete Mathematics Group - ECPv6.17.3//NONSGML v1.0//EN
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X-WR-CALNAME:Discrete Mathematics Group
X-ORIGINAL-URL:https://dimag.ibs.re.kr
X-WR-CALDESC:Events for Discrete Mathematics Group
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BEGIN:VTIMEZONE
TZID:Asia/Seoul
BEGIN:STANDARD
TZOFFSETFROM:+0900
TZOFFSETTO:+0900
TZNAME:KST
DTSTART:20250101T000000
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BEGIN:VEVENT
DTSTART;TZID=Asia/Seoul:20260901T163000
DTEND;TZID=Asia/Seoul:20260901T173000
DTSTAMP:20260801T015407Z
CREATED:20260801T015407Z
LAST-MODIFIED:20260801T015407Z
UID:13026-1788280200-1788283800@dimag.ibs.re.kr
SUMMARY:Ben Lund\, TBA
DESCRIPTION:
URL:https://dimag.ibs.re.kr/event/2026-09-01/
LOCATION:Room B332\, IBS (기초과학연구원)
CATEGORIES:Discrete Math Seminar
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Asia/Seoul:20260908T163000
DTEND;TZID=Asia/Seoul:20260908T173000
DTSTAMP:20260812T074452Z
CREATED:20260812T064149Z
LAST-MODIFIED:20260812T074452Z
UID:13089-1788885000-1788888600@dimag.ibs.re.kr
SUMMARY:Olga Medrano Martín del Campo\, TBA
DESCRIPTION:
URL:https://dimag.ibs.re.kr/event/2026-09-08/
LOCATION:Room B332\, IBS (기초과학연구원)
CATEGORIES:Discrete Math Seminar
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Asia/Seoul:20260915T163000
DTEND;TZID=Asia/Seoul:20260915T173000
DTSTAMP:20260821T131519Z
CREATED:20260821T131407Z
LAST-MODIFIED:20260821T131519Z
UID:13138-1789489800-1789493400@dimag.ibs.re.kr
SUMMARY:Gabriëlle Zwaneveld\, On Seymour-tight orientations
DESCRIPTION:I discuss ‘almost counterexamples’ to Seymour’s second neighbourhood conjecture. In what we call Seymour-tight orientations\, the size of the first neighbourhood of each vertex equals the size of its second neighbourhood. We give several examples and constructions. Specifically\, we prove that the class of Seymour-tight orientations is closed under taking (generalized) lexicographic products. Moreover\, the lexicographic product of a putative counterexample to Seymour’s second neighbourhood conjecture and a Seymour-tight orientation is again a counterexample. \nUsing lexicographic products\, we show that if the conjecture is false\, then there exist counterexamples that are close to regular tournaments\, and moreover that any digraph occurs as an induced subgraph of a counterexample. We then use this same machinery to construct special putative counterexamples to Sullivan’s conjecture. \nThe inherent symmetry of these orientations give access to an algebraic perspective. Seymour-tight orientations that are also Cayley digraphs correspond to special pairs of critical sets in groups\, which connects potentially to additive combinatorics. We use Kemperman’s theorem to characterize those Seymour-tight orientations that are the Cayley digraph of an abelian group.
URL:https://dimag.ibs.re.kr/event/2026-09-15/
LOCATION:Room B332\, IBS (기초과학연구원)
CATEGORIES:Discrete Math Seminar
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Asia/Seoul:20260922T163000
DTEND;TZID=Asia/Seoul:20260922T173000
DTSTAMP:20260802T034024Z
CREATED:20260717T080520Z
LAST-MODIFIED:20260802T034024Z
UID:12910-1790094600-1790098200@dimag.ibs.re.kr
SUMMARY:David Wood\, Proof of the Clustered Hadwiger Conjecture
DESCRIPTION:Hadwiger famously conjectured that every $K_h$-minor-free graph is properly $(h-1)$-colourable. This talk will present the following improper analogue of Hadwiger’s Conjecture: for fixed $h$\, every $K_h$-minor-free graph is $(h-1)$-colourable with monochromatic components of bounded size. The number of colours is best possible regardless of the size of monochromatic components. This solves an open problem of Edwards\, Kang\, Kim\, Oum and Seymour [SIAM J. Disc. Math. 2015]\, and concludes a line of research initiated in 2007. Similarly\, for fixed $t\geqslant s$\, we show that every $K_{s\,t}$-minor-free graph is $(s+1)$-colourable with monochromatic components of bounded size. The number of colours is best possible\, solving an open problem of van de Heuvel and Wood [J. London Math. Soc. 2018]. We actually prove a single theorem from which both of the above results are immediate corollaries. For an excluded apex minor\, the result is strengthened  as follows: for fixed $t \geqslant s \geqslant 3$\, and for any fixed apex graph $X$\, every $K_{s\,t}$-subgraph-free $X$-minor-free graph is $(s+1)$-colourable with monochromatic components of bounded size. The number of colours is again best possible. This is joint work with Vida Dujmović\, Louis Esperet and Pat Morin [arXiv:2306.06224].
URL:https://dimag.ibs.re.kr/event/2026-09-22/
LOCATION:Room B332\, IBS (기초과학연구원)
CATEGORIES:Discrete Math Seminar
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Asia/Seoul:20261006T163000
DTEND;TZID=Asia/Seoul:20261006T173000
DTSTAMP:20260821T005558Z
CREATED:20260821T005539Z
LAST-MODIFIED:20260821T005558Z
UID:13133-1791304200-1791307800@dimag.ibs.re.kr
SUMMARY:Daniel McGinnis\, Multi-generic initial ideals\, regularity\, and the optimal colorful fractional Helly theorem for $d$-Leray complexes
DESCRIPTION:A celebrated result of Bayer and Stillman from 1987 states that for a homogeneous ideal $I$ of a polynomial ring $S$\, the regularities of $S/I$ and $S/\textrm{GIN}(I)$ are the same under the reverse lexicographic monomial ordering\, where $\textrm{GIN}(I)$ is the generic initial ideal. If $R$ is a polynomial ring whose variables are subdivided into disjoint blocks of variables $X_1\,\dots\,X_c$\, there is a natural multi-grading on $R$\, and one can analogously define a multi-graded version of the generic initial ideal for any multi-homogeneous ideal $I$ of $R$. However\, the full strength of the Bayer-Stillman Theorem fails in the multi-graded setting; there are multi-homogeneous ideals $I$ such that the regularities are not preserved after passing to the multi-graded generic initial ideal no matter the choice of monomial ordering. \nWe prove lower bounds on the regularity of $R/I$ in terms of almost regular sequences of the multi-graded generic initial ideal of $I$ restricted to each block of variables. Again\, we use the reverse lexicographic monomial ordering\, but interestingly\, the lower bound result requires a particular choice of ordering on the variables. \nAs an application\, we prove the optimal fractional Helly theorem for $d$-Leray simplicial complexes\, a problem stemming from the work of Kim in 2017.
URL:https://dimag.ibs.re.kr/event/2026-10-06/
LOCATION:Room B332\, IBS (기초과학연구원)
CATEGORIES:Discrete Math Seminar
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BEGIN:VEVENT
DTSTART;TZID=Asia/Seoul:20261013T163000
DTEND;TZID=Asia/Seoul:20261013T173000
DTSTAMP:20260819T090026Z
CREATED:20260811T214705Z
LAST-MODIFIED:20260819T090026Z
UID:13078-1791909000-1791912600@dimag.ibs.re.kr
SUMMARY:Julien Codsi\, Recent progress in the tree-⍺ world
DESCRIPTION:Treewidth is a graph parameter commonly used to quantify how “close” a graph is to a tree. Although it is a cornerstone of structural graph theory and algorithm design\, it is nearly useless for algorithmic purposes in many dense graph classes. In this talk\, we discuss the tree-independence number\, a more versatile graph parameter that replaces the standard width measure with the stability number. We will present recent results aimed at characterizing the graph classes in which this parameter enables sub-exponential time algorithms for problems that are\, in general\, NP-hard.
URL:https://dimag.ibs.re.kr/event/2026-10-13/
LOCATION:Room B332\, IBS (기초과학연구원)
CATEGORIES:Discrete Math Seminar
END:VEVENT
BEGIN:VEVENT
DTSTART;VALUE=DATE:20261020
DTEND;VALUE=DATE:20261023
DTSTAMP:20260702T064849Z
CREATED:20260611T134208Z
LAST-MODIFIED:20260702T064849Z
UID:12748-1792454400-1792713599@dimag.ibs.re.kr
SUMMARY:2026 Combinatorics Workshop (2026 조합론 학술대회)
DESCRIPTION:Combinatorics Workshop (조합론 학술대회) is an annual conference for researchers in combinatorics and related areas in Korea. It was started in 2004 by the Yonsei University BK21 Research Group. Since 2013\, this workshop has been advised by the committee of discrete mathematics of the Korean Mathematical Society. \nWebsite: https://cw2026.combinatorics.kr/en/ \nVenue\nKonjiam Resort\, EW Village\, B2\, Meeting Room OPUS2 \n(278\, Docheogwit-Ro\, Docheok-Myeon\, Gwangju-Si\, Gyeonggi-Do\, Korea) \n\nTravel Instructions\n\nDates\nOctober 20 to 22\, 2026 \nPlenary Speaker\nAlexander V. Kostochka (UIUC) \nInvited Speakers\n\nCheolwon Heo (SUNY Korea)\nTony Huynh (IBS DIMAG)\nDabeen Lee (Seoul National University)\nJongbaek Song (Pusan National University)\n\nContributed Talks\nEach contributed talk will be about 20 minutes\, including questions. Please note that we may stop accepting contributed talk applications before the deadline if all available slots are filled. \nIf you are interested in giving a contributed talk at the workshop\, please submit an abstract by August 31\, 2026. \nTo apply for a contributed talk\, go to Call for Abstracts on Indico and click “Submit new abstract.” You may need to create an IBS Indico account. \nRegistration\nRegistration link \nThe registration deadline is August 31\, 2026. \nOrganizing Committee\n\nIlkyoo Choi (최일규)\, Hankuk University of Foreign Studies\, IBS Discrete Mathematics Group\, KIAS\nSang-il Oum (엄상일)\, IBS Discrete Mathematics Group\nBoram Park (박보람)\, Seoul National University\n\nAdvisory Committee\nCommittee of Discrete Mathematics\, The Korean Mathematical Society (Chair: Sang-il Oum) \nSponsors\n\nIBS Discrete Mathematics Group\nKorean Mathematical Society\nSeoul National University\nHankuk University of Foreign Studies
URL:https://dimag.ibs.re.kr/event/2026-combinatorics-workshop/
LOCATION:Konjiam Resort\, EW Village\, B2\, Meeting Room OPUS2
CATEGORIES:Workshops and Conferences
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