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PRODID:-//Discrete Mathematics Group - ECPv6.15.20//NONSGML v1.0//EN
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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:20240101T000000
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BEGIN:VEVENT
DTSTART;VALUE=DATE:20250210
DTEND;VALUE=DATE:20250213
DTSTAMP:20260416T025034
CREATED:20250121T050854Z
LAST-MODIFIED:20250121T050854Z
UID:10460-1739145600-1739404799@dimag.ibs.re.kr
SUMMARY:IBS-DIMAG Winter School on Graph Minors\, Week 2
DESCRIPTION:
URL:https://dimag.ibs.re.kr/event/graph-minors-week-2/
LOCATION:Room B109\, IBS (기초과학연구원)
CATEGORIES:Workshops and Conferences
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Asia/Seoul:20250211T163000
DTEND;TZID=Asia/Seoul:20250211T173000
DTSTAMP:20260416T025034
CREATED:20241226T073216Z
LAST-MODIFIED:20250119T115501Z
UID:10327-1739291400-1739295000@dimag.ibs.re.kr
SUMMARY:Jungho Ahn (안정호)\, A coarse Erdős-Pósa theorem for constrained cycles
DESCRIPTION:An induced packing of cycles in a graph is a set of vertex-disjoint cycles such that the graph has no edge between distinct cycles of the set. The classic Erdős-Pósa theorem shows that for every positive integer $k$\, every graph contains $k$ vertex-disjoint cycles or a set of $O(k\log k)$ vertices which intersects every cycle of $G$. \nWe generalise this classic Erdős-Pósa theorem to induced packings of cycles of length at least $\ell$ for any integer $\ell$. We show that there exists a function $f(k\,\ell)=O(\ell k\log k)$ such that for all positive integers $k$ and $\ell$ with $\ell\geq3$\, every graph $G$ contains an induced packing of $k$ cycles of length at least $\ell$ or a set $X$ of at most $f(k\,\ell)$ vertices such that the closed neighbourhood of $X$ intersects every cycle of $G$. \nFurthermore\, we extend the result to long cycles containing prescribed vertices. For a graph $G$ and a set $S\subseteq V(G)$\, an $S$-cycle in $G$ is a cycle containing a vertex in $S$. We show that for all positive integers $k$ and $\ell$ with $\ell\geq3$\, every graph $G$\, and every set $S\subseteq V(G)$\, $G$ contains an induced packing of $k$ $S$-cycles of length at least $\ell$ or a set $X$ of at most $\ell k^{O(1)}$ vertices such that the closed neighbourhood of $X$ intersects every cycle of $G$. \nOur proofs are constructive and yield polynomial-time algorithms\, for fixed $\ell$\, finding either the induced packing of the constrained cycles or the set $X$. \nThis is based on joint works with Pascal Gollin\, Tony Huynh\, and O-joung Kwon.
URL:https://dimag.ibs.re.kr/event/2025-02-11/
LOCATION:Room B332\, IBS (기초과학연구원)
CATEGORIES:Discrete Math Seminar
END:VEVENT
BEGIN:VEVENT
DTSTART;VALUE=DATE:20250217
DTEND;VALUE=DATE:20250220
DTSTAMP:20260416T025034
CREATED:20250121T051001Z
LAST-MODIFIED:20250121T051001Z
UID:10462-1739750400-1740009599@dimag.ibs.re.kr
SUMMARY:IBS-DIMAG Winter School on Graph Minors\, Week 3
DESCRIPTION:
URL:https://dimag.ibs.re.kr/event/graph-minors-week-3/
LOCATION:Room B109\, IBS (기초과학연구원)
CATEGORIES:Workshops and Conferences
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Asia/Seoul:20250218T163000
DTEND;TZID=Asia/Seoul:20250218T173000
DTSTAMP:20260416T025034
CREATED:20250123T111843Z
LAST-MODIFIED:20250123T111843Z
UID:10488-1739896200-1739899800@dimag.ibs.re.kr
SUMMARY:O-joung Kwon (권오정)\, Erdős-Pósa property of A-paths in unoriented group-labelled graphs
DESCRIPTION:A family $\mathcal{F}$ of graphs is said to satisfy the Erdős-Pósa property if there exists a function $f$ such that for every positive integer $k$\, every graph $G$ contains either $k$ (vertex-)disjoint subgraphs in $\mathcal{F}$ or a set of at most $f(k)$ vertices intersecting every subgraph of $G$ in $\mathcal{F}$. We characterize the obstructions to the Erdős-Pósa property of $A$-paths in unoriented group-labelled graphs. As a result\, we prove that for every finite abelian group $\Gamma$ and for every subset $\Lambda$ of $\Gamma$\, the family of $\Gamma$-labelled $A$-paths whose lengths are in $\Lambda$ satisfies the half-integral relaxation of the Erdős-Pósa property. Moreover\, we give a characterization of such $\Gamma$ and $\Lambda\subseteq\Gamma$ for which the same family of $A$-paths satisfies the full Erdős-Pósa property. This is joint work with Youngho Yoo.
URL:https://dimag.ibs.re.kr/event/2025-02-18/
LOCATION:Room B332\, IBS (기초과학연구원)
CATEGORIES:Discrete Math Seminar
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Asia/Seoul:20250225T163000
DTEND;TZID=Asia/Seoul:20250225T173000
DTSTAMP:20260416T025034
CREATED:20250104T011404Z
LAST-MODIFIED:20250214T002236Z
UID:10354-1740501000-1740504600@dimag.ibs.re.kr
SUMMARY:Sepehr Hajebi\, The pathwidth theorem for induced subgraphs
DESCRIPTION:We present a full characterization of the unavoidable induced subgraphs of graphs with large pathwidth. This consists of two results. The first result says that for every forest H\, every graph of sufficiently large pathwidth contains either a large complete subgraph\, a large complete bipartite induced minor\, or an induced minor isomorphic to H. The second result describes the unavoidable induced subgraphs of graphs with a large complete bipartite induced minor. \nWe will also try to discuss the proof of the first result with as much detail as time permits. \nBased on joint work with Maria Chudnovsky and Sophie Spirkl.
URL:https://dimag.ibs.re.kr/event/2025-02-25/
LOCATION:Room B332\, IBS (기초과학연구원)
CATEGORIES:Discrete Math Seminar
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Asia/Seoul:20250304T163000
DTEND;TZID=Asia/Seoul:20250304T173000
DTSTAMP:20260416T025034
CREATED:20250123T112518Z
LAST-MODIFIED:20250223T142525Z
UID:10492-1741105800-1741109400@dimag.ibs.re.kr
SUMMARY:Irene Muzi\, An elementary bound for Younger's conjecture
DESCRIPTION:In 1996\, Reed\, Robertson\, Seymour and Thomas proved Younger’s Conjecture\, which states that for all directed graphs D\, there exists a function f such that if D does not contain k disjoint cycles\, D contains a feedback vertex set\, i.e. a subset of vertices whose deletion renders the graph acyclic\, of size bounded by f(k). However\, the function obtained by Reed\, Robertson\, Seymour and Thomas is enormous and\, in fact\, not even elementary. The bound had\, so far\, not been improved. In this talk\, I will present new techniques to improve the bound from non-elementary to elementary. This is joint work with Meike Hatzel\, Stephan Kreutzer and Marcelo Milani.
URL:https://dimag.ibs.re.kr/event/2025-03-04/
LOCATION:Room B332\, IBS (기초과학연구원)
CATEGORIES:Discrete Math Seminar
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Asia/Seoul:20250311T163000
DTEND;TZID=Asia/Seoul:20250311T173000
DTSTAMP:20260416T025034
CREATED:20240909T194937Z
LAST-MODIFIED:20250218T150344Z
UID:9870-1741710600-1741714200@dimag.ibs.re.kr
SUMMARY:Johannes Carmesin\, Open problems in graph theory
DESCRIPTION:Since the proof of the graph minor structure theorem by Robertson and Seymour in 2004\, its underlying ideas have found applications in a much broader range of settings than their original context. They have driven profound progress in areas such as vertex minors\, pivot minors\, matroids\, directed graphs\, and 2-dimensional simplicial complexes. In this talk\, I will present three open problems related to this development\, each requiring some background.
URL:https://dimag.ibs.re.kr/event/2025-03-11/
LOCATION:Room B332\, IBS (기초과학연구원)
CATEGORIES:Discrete Math Seminar
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Asia/Seoul:20250318T163000
DTEND;TZID=Asia/Seoul:20250318T173000
DTSTAMP:20260416T025034
CREATED:20250205T073256Z
LAST-MODIFIED:20250305T204931Z
UID:10539-1742315400-1742319000@dimag.ibs.re.kr
SUMMARY:Michał Seweryn\, Dimension and standard examples in planar posets
DESCRIPTION:The dimension of a poset is the least integer $d$ such that the poset is isomorphic to a subposet of the product of $d$ linear orders. In 1983\, Kelly constructed planar posets of arbitrarily large dimension. Crucially\, the posets in his construction involve large standard examples\, the canonical structure preventing a poset from having small dimension. Kelly’s construction inspired one of the most challenging questions in dimension theory: are large standard examples unavoidable in planar posets of large dimension? We answer the question affirmatively by proving that every $d$-dimensional planar poset contains a standard example of order $\Omega(d)$. More generally\, we prove that every poset from Kelly’s construction appears in every poset with a planar cover graph of sufficiently large dimension. \njoint work with Heather Smith Blake\, Jędrzej Hodor\, Piotr Micek\, and William T. Trotter.
URL:https://dimag.ibs.re.kr/event/2025-03-18/
LOCATION:Room B332\, IBS (기초과학연구원)
CATEGORIES:Discrete Math Seminar
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Asia/Seoul:20250401T163000
DTEND;TZID=Asia/Seoul:20250401T173000
DTSTAMP:20260416T025034
CREATED:20250310T023035Z
LAST-MODIFIED:20250310T023155Z
UID:10673-1743525000-1743528600@dimag.ibs.re.kr
SUMMARY:Hyunwoo Lee (이현우)\, Reconstructing hypergraph matching polynomials
DESCRIPTION:By utilizing the recently developed hypergraph analogue of Godsil’s identity by the second author\, we prove that for all $n \geq k \geq 2$\, one can reconstruct the matching polynomial of an $n$-vertex $k$-uniform hypergraph from the multiset of all induced sub-hypergraphs on $\lfloor \frac{k-1}{k}n \rfloor + 1$ vertices. This generalizes the well-known result of Godsil on graphs in 1981 to every uniform hypergraph. As a corollary\, we show that for every graph $F$\, one can reconstruct the number of $F$-factors in a graph under analogous conditions. We also constructed examples that imply the number $\lfloor \frac{k-1}{k}n \rfloor + 1$ is the best possible for all $n\geq k \geq 2$ with $n$ divisible by $k$. This is joint work Donggyu Kim.
URL:https://dimag.ibs.re.kr/event/2025-04-01/
LOCATION:Room B332\, IBS (기초과학연구원)
CATEGORIES:Discrete Math Seminar
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Asia/Seoul:20250408T163000
DTEND;TZID=Asia/Seoul:20250408T173000
DTSTAMP:20260416T025034
CREATED:20250210T063056Z
LAST-MODIFIED:20250331T224202Z
UID:10560-1744129800-1744133400@dimag.ibs.re.kr
SUMMARY:Marcelo Garlet Milani\, Cycles of Well-Linked Sets and an Elementary Bound for the Directed Grid Theorem
DESCRIPTION:In 2015\, Kawarabayashi and Kreutzer proved the directed grid theorem. The theorem states the existence of a function f such that every digraph of directed tree-width f(k) contains a cylindrical grid of order k as a butterfly minor\, but the given function grows non-elementarily with the size of the grid minor. \nWe present an alternative proof of the directed grid theorem\, first proven by Kawarabayashi and Kreutzer in 2015\, which is conceptually much simpler\, more modular in its composition and also improves the upper bound for the function f to a power tower of height 22. \nOur proof is inspired by the breakthrough result of Chekuri and Chuzhoy\, who proved a polynomial bound for the excluded grid theorem for undirected graphs. We translate a key concept of their proof to directed graphs by introducing cycles of well-linked sets (CWS)\, and show that any digraph of high directed tree-width contains a large CWS\, which in turn contains a large cylindrical grid. \nThis is joint work with Meike Hatzel\, Stephan Kreutzer and Irene Muzi.
URL:https://dimag.ibs.re.kr/event/2025-04-08/
LOCATION:Room B332\, IBS (기초과학연구원)
CATEGORIES:Discrete Math Seminar
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Asia/Seoul:20250414T110000
DTEND;TZID=Asia/Seoul:20250414T120000
DTSTAMP:20260416T025034
CREATED:20250218T063907Z
LAST-MODIFIED:20250318T144436Z
UID:10608-1744628400-1744632000@dimag.ibs.re.kr
SUMMARY:Daniel McGinnis\, A necessary and sufficient condition for $k$-transversals
DESCRIPTION:We solve a long-standing open problem posed by Goodman and Pollack in 1988 by establishing a necessary and sufficient condition for a finite family of convex sets in $\mathbb{R}^d$ to admit a $k$-transversal (a $k$-dimensional affine subspace that intersects each set) for any $0 \le k \le d-1$. This result is a common generalization of Helly’s theorem ($k=0$) and the Goodman-Pollack-Wenger theorem ($k=d-1$). \nThis is joint work with Nikola Sadovek.
URL:https://dimag.ibs.re.kr/event/2025-04-14/
LOCATION:Room B332\, IBS (기초과학연구원)
CATEGORIES:Discrete Math Seminar
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Asia/Seoul:20250415T163000
DTEND;TZID=Asia/Seoul:20250415T173000
DTSTAMP:20260416T025034
CREATED:20250211T042237Z
LAST-MODIFIED:20250331T222415Z
UID:10569-1744734600-1744738200@dimag.ibs.re.kr
SUMMARY:Nicola Lorenz\, A Minor Characterisation of Normally Spanned Sets of Vertices
DESCRIPTION:A rooted spanning tree of a graph $G$ is called normal if the endvertices of all edges of $G$ are comparable in the tree order. It is well known that every finite connected graph has a normal spanning tree (also known as depth-first search tree). Also\, all countable graphs have normal spanning trees\, but uncountable complete graphs for example do not. In 2021\, Pitz proved the following characterisation for graphs with normal spanning trees\, which had been conjectured by Halin: A connected graph $G$ has a normal spanning tree if and only if every minor of $G$ has countable colouring number\, i.e. there is a well-order of the vertices such that every vertex is preceded by only finitely many of its neighbours. \nMore generally\, a not necessarily spanning tree in $G$ is called normal if for every path $P$ in $G$ with both endvertices in $T$ but no inner vertices in $T$\, the endvertices of $P$ are comparable in the tree order. We establish a local version of Pitz’s theorem by characterising for which sets $U$ of vertices of $G$ there is a normal tree in $G$ covering $U$. The results are joint work with Max Pitz.
URL:https://dimag.ibs.re.kr/event/2025-04-15/
LOCATION:Room B332\, IBS (기초과학연구원)
CATEGORIES:Discrete Math Seminar
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Asia/Seoul:20250422T163000
DTEND;TZID=Asia/Seoul:20250422T173000
DTSTAMP:20260416T025034
CREATED:20250210T062933Z
LAST-MODIFIED:20250414T092141Z
UID:10558-1745339400-1745343000@dimag.ibs.re.kr
SUMMARY:Marcin Briański\, Burling Graphs as (almost) universal obstacles to  $\chi$-boundedness
DESCRIPTION:What causes a graph to have high chromatic number? One obvious reason is containing a large clique (a set of pairwise adjacent vertices). This naturally leads to investigation of \(\chi\)-bounded classes of graphs — classes where a large clique is essentially the only reason for large chromatic number. \nUnfortunately\, many interesting graph classes are not \(\chi\)-bounded. An eerily common obstruction to being \(\chi\)-bounded are the Burling graphs — a family of triangle-free graphs with unbounded chromatic number. These graphs have served as counterexamples in many settings: demonstrating that graphs excluding an induced subdivision of \(K_{5}\) are not \(\chi\)-bounded\, that string graphs are not \(\chi\)-bounded\, that intersection graphs of boxes in \({\mathbb{R}}^{3}\) are not \(\chi\)-bounded\, and many others. \nIn many of these cases\, this sequence is the only known obstruction to \(\chi\)-boundedness. This led Chudnovsky\, Scott\, and Seymour to conjecture that any graph of sufficiently high chromatic number must either contain a large clique\, an induced proper subdivision of a clique\, or a large Burling graph as an induced subgraph. \nThe prevailing belief was that this conjecture should be false. Somewhat surprisingly\, we did manage to prove it under an extra assumption on the “locality” of the chromatic number — that the input graph belongs to a \(2\)-controlled family of graphs\, where a high chromatic number is always certified by a ball of radius \(2\) with large chromatic number. \nIn this talk\, I will present this result and discuss its implications in structural graph theory\, and algorithmic implications to colouring problems in specific graph families. \nThis talk is based on joint work with Tara Abrishami\, James Davies\, Xiying Du\, Jana Masaříková\, Paweł Rzążewski\, and Bartosz Walczak conducted during the STWOR2 workshop in Chęciny Poland.
URL:https://dimag.ibs.re.kr/event/2025-04-22/
LOCATION:Room B332\, IBS (기초과학연구원)
CATEGORIES:Discrete Math Seminar
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Asia/Seoul:20250428T110000
DTEND;TZID=Asia/Seoul:20250428T120000
DTSTAMP:20260416T025034
CREATED:20250417T134915Z
LAST-MODIFIED:20250418T012250Z
UID:10801-1745838000-1745841600@dimag.ibs.re.kr
SUMMARY:Pascal Schweitzer\, Recent insights surrounding combinatorial approaches to isomorphism and symmetry problems
DESCRIPTION:Modern practical software libraries that are designed for isomorphism tests and symmetry computation rely on combinatorial techniques combined with techniques from algorithmic group theory. The Weisfeiler-Leman algorithm is such a combinatorial technique. When taking a certain view from descriptive complexity theory\, the algorithm is universal. After an introduction to problems arising in symmetry computation and this particular combinatorial technique\, I will give an overview of results from recent years. The results give insights into worst-case behavior and computational complexity.
URL:https://dimag.ibs.re.kr/event/2025-04-28/
LOCATION:Room B332\, IBS (기초과학연구원)
CATEGORIES:Discrete Math Seminar
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Asia/Seoul:20250429T163000
DTEND;TZID=Asia/Seoul:20250429T173000
DTSTAMP:20260416T025034
CREATED:20250212T111256Z
LAST-MODIFIED:20250212T112909Z
UID:10581-1745944200-1745947800@dimag.ibs.re.kr
SUMMARY:Eunjin Oh (오은진)\, Approximation Algorithms for the Geometric Multimatching Problem
DESCRIPTION:Let S and T be two sets of points in a metric space with a total of n points. Each point in S and T has an associated value that specifies an upper limit on how many points it can be matched with from the other set. A multimatching between S and T is a way of pairing points such that each point in S is matched with at least as many points in T as its assigned value\, and vice versa for each point in T. The cost of a multimatching is defined as the sum of the distances between all matched pairs of points. The geometric multimatching problem seeks to find a multimatching that minimizes this cost. A special case where each point is matched to at most one other point is known as the geometric many-to-many matching problem. \nWe present two results for these problems when the underlying metric space has a bounded doubling dimension. Specifically\, we provide the first near-linear-time approximation scheme for the geometric multimatching problem in terms of the output size. Additionally\, we improve upon the best-known approximation algorithm for the geometric many-to-many matching problem\, previously introduced by Bandyapadhyay and Xue (SoCG 2024)\, which won the best paper award at SoCG 2024. \nThis is joint work with Shinwoo An and Jie Xue.
URL:https://dimag.ibs.re.kr/event/2025-04-29/
LOCATION:Room B332\, IBS (기초과학연구원)
CATEGORIES:Discrete Math Seminar
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Asia/Seoul:20250513T163000
DTEND;TZID=Asia/Seoul:20250513T173000
DTSTAMP:20260416T025034
CREATED:20250218T070323Z
LAST-MODIFIED:20250310T022916Z
UID:10617-1747153800-1747157400@dimag.ibs.re.kr
SUMMARY:Seokbeom Kim (김석범)\, The structure of △(1\, 2\, 2)-free tournaments
DESCRIPTION:Given a tournament $S$\, a tournament is $S$-free if it has no subtournament isomorphic to $S$. Until now\, there have been only a small number of tournaments $S$ such that the complete structure of $S$-free tournaments is known. \nLet $\triangle(1\, 2\, 2)$ be a tournament obtained from the cyclic triangle by substituting two-vertex tournaments for two of its vertices. In this talk\, we present a structure theorem for $\triangle(1\, 2\, 2)$-free tournaments\, which was previously unknown. As an application\, we provide tight bounds for the chromatic number as well as the size of the largest transitive subtournament for such tournaments. \nThis talk is based on joint work with Taite LaGrange\, Mathieu Rundström\, Arpan Sadhukhan\, and Sophie Spirkl.
URL:https://dimag.ibs.re.kr/event/2025-05-13/
LOCATION:Room B332\, IBS (기초과학연구원)
CATEGORIES:Discrete Math Seminar
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Asia/Seoul:20250527T163000
DTEND;TZID=Asia/Seoul:20250527T173000
DTSTAMP:20260416T025034
CREATED:20250415T051555Z
LAST-MODIFIED:20250517T114823Z
UID:10778-1748363400-1748367000@dimag.ibs.re.kr
SUMMARY:Meike Hatzel\, Counterexample to Babai's lonely colour conjecture
DESCRIPTION:Motivated by colouring minimal Cayley graphs\, in 1978 Babai conjectured that no-lonely-colour graphs have bounded chromatic number. We disprove this in a strong sense by constructing graphs of arbitrarily large girth and chromatic number that have a proper edge colouring in which each cycle contains no colour exactly once. \nThe result presented is the joint work with James Davies and Liana Yepremyan.
URL:https://dimag.ibs.re.kr/event/2025-05-27/
LOCATION:Room B332\, IBS (기초과학연구원)
CATEGORIES:Discrete Math Seminar
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Asia/Seoul:20250604T163000
DTEND;TZID=Asia/Seoul:20250604T173000
DTSTAMP:20260416T025034
CREATED:20250319T134432Z
LAST-MODIFIED:20250603T071758Z
UID:10696-1749054600-1749058200@dimag.ibs.re.kr
SUMMARY:Denys Bulavka\, Strict Erdős-Ko-Rado Theorems for Simplicial Complexes
DESCRIPTION:The now classical theorem of Erdős\, Ko and Rado establishes\nthe size of a maximal uniform family of pairwise-intersecting sets as well as a characterization of the families attaining such upper bound. One natural extension of this theorem is that of restricting the possiblechoices for the sets. That is\, given a simplicial complex\, what is the size of a maximal uniform family of pairwise-intersecting faces. Holroyd and Talbot\, and Borg conjectured that the same phenomena as in the classical case (i.e.\, the simplex) occurs: there is a maximal size pairwise-intersecting family with all its faces having some common vertex. Under stronger hypothesis\, they also conjectured that if a family attains such bound then its members must have a common vertex. In this talk I will present some progress towards the characterization of the maximal families. Concretely I will show that the conjecture is true for near-cones of sufficiently high depth. In particular\, this implies that the characterization of maximal families holds for\, for example\, the independence complex of a chordal graph with an isolated vertex as well as the independence complex of a (large enough) disjoint union of graphs with at least one isolated vertex. Under stronger hypothesis\, i.e.\, more isolated vertices\, we also recover a stability theorem. \nThis talk is based on a joint work with Russ Woodroofe.
URL:https://dimag.ibs.re.kr/event/2025-06-04/
LOCATION:Room B332\, IBS (기초과학연구원)
CATEGORIES:Discrete Math Seminar
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Asia/Seoul:20250610T163000
DTEND;TZID=Asia/Seoul:20250610T173000
DTSTAMP:20260416T025034
CREATED:20250407T060939Z
LAST-MODIFIED:20250408T065935Z
UID:10754-1749573000-1749576600@dimag.ibs.re.kr
SUMMARY:On-Hei Solomon Lo\, Minors of non-hamiltonian graphs
DESCRIPTION:A seminal result of Tutte asserts that every 4-connected planar graph is hamiltonian. By Wagner’s theorem\, Tutte’s result can be restated as: every 4-connected graph with no $K_{3\,3}$ minor is hamiltonian. In 2018\, Ding and Marshall posed the problem of characterizing the minor-minimal 3-connected non-hamiltonian graphs. They conjectured that every 3-connected non-hamiltonian graph contains a minor of $K_{3\,4}$\, $\mathfrak{Q}^+$\, or the Herschel graph\, where $\mathfrak{Q}^+$ is obtained from the cube by adding a new vertex and connecting it to three vertices that share a common neighbor in the cube. We recently resolved this conjecture along with some related problems. In this talk\, we review the background and discuss the proof.
URL:https://dimag.ibs.re.kr/event/2025-06-10/
LOCATION:Room B332\, IBS (기초과학연구원)
CATEGORIES:Discrete Math Seminar
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Asia/Seoul:20250617T163000
DTEND;TZID=Asia/Seoul:20250617T173000
DTSTAMP:20260416T025034
CREATED:20250428T140029Z
LAST-MODIFIED:20250428T140029Z
UID:10877-1750177800-1750181400@dimag.ibs.re.kr
SUMMARY:Attila Jung\, The Quantitative Fractional Helly Theorem
DESCRIPTION:Two celebrated extensions of Helly’s theorem are the Fractional Helly theorem of Katchalski and Liu (1979) and the Quantitative Volume theorem of Barany\, Katchalski\, and Pach (1982). Improving on several recent works\, we prove an optimal combination of these two results. We show that given a family $F$ of $n$ convex sets in $\mathbb{R}^d$ such that at least $\alpha \binom{n}{d+1}$ of the $(d+1)$-tuples of $F$ have an intersection of volume at least 1\, then one can select $\Omega_{d\,\alpha}(n)$ members of $F$ whose intersection has volume at least $\Omega_d(1)$. Joint work with Nora Frankl and Istvan Tomon.
URL:https://dimag.ibs.re.kr/event/2025-06-17/
LOCATION:Room B332\, IBS (기초과학연구원)
CATEGORIES:Discrete Math Seminar
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Asia/Seoul:20250625T163000
DTEND;TZID=Asia/Seoul:20250625T173000
DTSTAMP:20260416T025034
CREATED:20250606T142052Z
LAST-MODIFIED:20250611T082038Z
UID:10973-1750869000-1750872600@dimag.ibs.re.kr
SUMMARY:Roohani Sharma\, Uniform and Constructive Polynomial Kernel for Deletion to $K_{2\,p}$ Minor-Free Graphs
DESCRIPTION:Let $\mathcal F$ be a fixed\, finite family of graphs. In the $\mathcal F$-Deletion problem\, the input is a graph G and a positive integer k\, and the goal is to determine if there exists a set of at most k vertices whose deletion results in a graph that does not contain any graph of $\mathcal F$ as a minor. The $\mathcal F$-Deletion problem encapsulates a large class of natural and interesting graph problems like Vertex Cover\, Feedback Vertex Set\, Treewidth-$\eta$ Deletion\, Treedepth-$\eta$ Deletion\, Pathwidth-$\eta$ Deletion\, Outerplanar Deletion\, Vertex Planarization and many more. We study the $\mathcal F$-Deletion problem from the kernelization perspective. \nIn a seminal work\, Fomin\, Lokshtanov\, Misra & Saurabh [FOCS 2012] gave a polynomial kernel for this problem when the family F contains at least one planar graph. The asymptotic growth of the size of the kernel is not uniform with respect to the family $\mathcal F$: that is\, the size of the kernel is $k^{f(\mathcal F)}$\, for some function f that depends only on $\mathcal F$. Also the size of the kernel depends on non-constructive constants. \nLater Giannopoulou\, Jansen\, Lokshtanov & Saurabh [TALG 2017] showed that the non-uniformity in the kernel size bound of Fomin et al. is unavoidable as Treewidth-$\eta$ Deletion\, cannot admit a kernel of size $O(k^{(\eta +1)/2 -\epsilon)}$\, for any $\epsilon >0$\, unless NP $\subseteq$ coNP/poly. On the other hand it was also shown that Treedepth-$\eta$ Deletion\, admits a uniform kernel of size $f(\mathcal F) k^6$\, showcasing that there are subclasses of $\mathcal F$ where the asymptotic kernel sizes do not grow as a function of the family $\mathcal F$. This work leads to the natural question of determining classes of $\mathcal F$ where the problem admits uniform polynomial kernels. \nIn this work\, we show that if all the graphs in $\mathcal F$ are connected and $\mathcal F$ contains $K_{2\,p}$ (a bipartite graph with 2 vertices on one side and p vertices on the other)\, then the problem admits a uniform kernel of size $f(\mathcal F) k^{10}$ where the constants in the size bound are also constructive. The graph $K_{2\,p}$ is one natural extension of the graph $\theta_p$\, where $\theta_p$ is a graph on two vertices and p parallel edges. The case when $\mathcal F$ contains $\theta_p$ has been studied earlier and serves as (the only) other example where the problem admits a uniform polynomial kernel. \nThis is joint work with William Lochet.
URL:https://dimag.ibs.re.kr/event/2025-06-25/
LOCATION:Room B332\, IBS (기초과학연구원)
CATEGORIES:Discrete Math Seminar
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Asia/Seoul:20250701T163000
DTEND;TZID=Asia/Seoul:20250701T173000
DTSTAMP:20260416T025034
CREATED:20250324T010911Z
LAST-MODIFIED:20250610T150051Z
UID:10713-1751387400-1751391000@dimag.ibs.re.kr
SUMMARY:Sergey Norin\, Asymptotic dimension of intersection graphs
DESCRIPTION:The notion of asymptotic dimension of metric spaces\, introduced by Gromov\, describes their large-scale behaviour. Asymptotic dimension of graph families has been recently studied\, in particular\, by Bonamy et al. who proved that the asymptotic dimension of proper minor-closed graph families is at most two. \nWe will discuss nerve-type theorems for asymptotic dimension. In particular\, we show that the asymptotic dimension of intersection graphs of balls and spheres in $\mathbb{R}^d$ is at most $d+1$. \nBased on joint work with Zdeněk Dvořák and with Chun-Hung Liu.
URL:https://dimag.ibs.re.kr/event/2025-07-01/
LOCATION:Room B332\, IBS (기초과학연구원)
CATEGORIES:Discrete Math Seminar
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Asia/Seoul:20250708T163000
DTEND;TZID=Asia/Seoul:20250708T173000
DTSTAMP:20260416T025034
CREATED:20250117T144850Z
LAST-MODIFIED:20250625T140926Z
UID:10409-1751992200-1751995800@dimag.ibs.re.kr
SUMMARY:Mihyun Kang (강미현)\, Phase transitions in a random subgraph of the hypercube
DESCRIPTION:We will discuss classical and recent results about phase transitions in random subgraphs of the hypercube and beyond. The focus will be on the giant component\, long cycles\, large matchings\, and isoperimetric properties.
URL:https://dimag.ibs.re.kr/event/2025-07-08/
LOCATION:Room B332\, IBS (기초과학연구원)
CATEGORIES:Discrete Math Seminar
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Asia/Seoul:20250714T140000
DTEND;TZID=Asia/Seoul:20250718T170000
DTSTAMP:20260416T025034
CREATED:20250421T055000Z
LAST-MODIFIED:20250706T061119Z
UID:10816-1752501600-1752858000@dimag.ibs.re.kr
SUMMARY:2025 Summer School on Combinatorics and Algorithms (2025 조합론 및 알고리즘 여름학교)
DESCRIPTION:The 2025 Summer School on Combinatorics and Algorithms is a venue for students and early-career researchers to learn selected topics in theoretical computer science and discrete mathematics. It will be a great opportunity for young and aspiring researchers to study topics which are important but not covered during the lectures in the university classes. \nWebsite: https://combialgo.dimag.kr/ \nLecturers and Topics\n\nÉdouard Bonnet\, LIP\, CNRS.\n\nInduced Subgraphs and Induced Minors of Graphs\n\n\nMichał Pilipczuk\, University of Warsaw.\n\nStructural Theory of Sparse Graphs\n\n\n\nSchedule\n\nStart on 14 July 2025 Monday\, 2 PM\nEnd on 18 July 2025 Friday\, 5 PM
URL:https://dimag.ibs.re.kr/event/2025-07-14/
LOCATION:POSTECH\, Pohang\, Korea
CATEGORIES:Workshops and Conferences
ORGANIZER;CN="Eunjung Kim (%EA%B9%80%EC%9D%80%EC%A0%95)":MAILTO:eunjungkim78@gmail.com
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Asia/Seoul:20250722T163000
DTEND;TZID=Asia/Seoul:20250722T173000
DTSTAMP:20260416T025034
CREATED:20250610T134044Z
LAST-MODIFIED:20250611T222217Z
UID:10983-1753201800-1753205400@dimag.ibs.re.kr
SUMMARY:Linda Cook\, A tight algorithmic meta-theorem for distributed certification within bounded treewidth graphs
DESCRIPTION:A local certification of a graph property is a protocol in which nodes are given  “certificates of a graph property” that allow the nodes to check whether their network has this property while only communicating with their local network. The key property of a local certification is that if certificates are corrupted\, some node in the network will be able to recognize this. Inspired by practical concerns\, the aim in LOCAL certification is to minimize the maximum size of a certificate. \nIn this talk we introduce local certification and open problems in the area and  present some recent joint work with Eunjung Kim and Tomáš Masařík\, A Tight Meta-theorem for LOCAL Certification of MSO2 Properties within Bounded Treewidth Graphs. \nIn this work\, instead of considering a specific graph property and developing a local certification protocol tailor-made for this property\, we aim for generic protocols that can certify any property expressible in a certain logical framework. We consider Monadic Second Order Logic (MSO$_2$)\, a powerful framework that can express properties such as non-$k$-colorability\, Hamiltonicity\, and $H$-minor-freeness. Unfortunately\, in general\, there are MSO$_2$-expressible properties that cannot be certified without huge certificates. For instance\, non-3-colorability requires certificates of size $\Omega(n^2/\log n)$ on general $n$-vertex graphs (Göös\, Suomela 2016). Hence\, we impose additional structural restrictions on the graph. Inspired by their importance in centralized computing and Robertson-Seymour Graph Minor theory\, we consider graphs of bounded treewidth. We provide a local certification protocol for certifying any MSO$_2$-expressible property on graphs of bounded treewidth and\, consequently\, a local certification protocol for certifying bounded treewidth. That is\, for each integer $k$ and each MSO$_2$-expressible property $\Pi$\, we give a local certification protocol to certify that a graph satisfies $\Pi$ and has treewidth at most $k$ using certificates of size $\mathcal{O}(\log n)$ (which is asymptotically optimal). Our result improves upon the works of Fraigniaud\, Montealegre\, Rapaport\, and Todinca (Algorithmica 2024)\,  Bousquet\, Feuilloley\, Pierron (PODC 2022)\, and the very recent work of Baterisna and Chang (PODC 2025).
URL:https://dimag.ibs.re.kr/event/2025-07-22/
LOCATION:Room B332\, IBS (기초과학연구원)
CATEGORIES:Discrete Math Seminar
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Asia/Seoul:20250729T163000
DTEND;TZID=Asia/Seoul:20250729T173000
DTSTAMP:20260416T025034
CREATED:20250706T060914Z
LAST-MODIFIED:20250707T012610Z
UID:11110-1753806600-1753810200@dimag.ibs.re.kr
SUMMARY:Colin Geniet\, Merge-width
DESCRIPTION:This talk is an introduction to the recent notion of merge-width\, proposed by Jan Dreier and Szymon Torúnczyk. I will give an overview of the context and motivations for merge-width\, namely the first-order model checking problem\, and present the definition\, some examples\, and some basic proof techniques with the example of χ-boundedness.\nThis is based on joint work with Marthe Bonamy.
URL:https://dimag.ibs.re.kr/event/2025-07-29/
LOCATION:Room B332\, IBS (기초과학연구원)
CATEGORIES:Discrete Math Seminar
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Asia/Seoul:20250805T163000
DTEND;TZID=Asia/Seoul:20250805T173000
DTSTAMP:20260416T025034
CREATED:20250713T060700Z
LAST-MODIFIED:20250725T225751Z
UID:11148-1754411400-1754415000@dimag.ibs.re.kr
SUMMARY:Tony Huynh\, Rainbow triangles and the Erdős-Hajnal problem in projective geometries
DESCRIPTION:We formulate a geometric version of the Erdős-Hajnal conjecture that applies to finite projective geometries rather than graphs.  In fact\, we give a natural extension of the ‘multicoloured’ version of the Erdős-Hajnal conjecture. Roughly\, our conjecture states that every colouring of the points of a finite projective geometry of dimension $n$ not containing a fixed colouring of a fixed projective geometry $H$ must contain a subspace of dimension polynomial in $n$ avoiding some colour. \nWhen $H$ is a ‘triangle’\, there are three different colourings\, all of which we resolve.  We handle the case that $H$ is a ‘rainbow’ triangle by proving that rainbow-triangle-free colourings of projective geometries are exactly those that admit a certain decomposition into two-coloured pieces. This is closely analogous to a theorem of Gallai on rainbow-triangle-free coloured complete graphs. The two non-rainbow colourings of $H$ are handled via a recent breakthrough result in additive combinatorics due to Kelley and Meka.  \nThis is joint work with Carolyn Chun\, James Dylan Douthitt\, Wayne Ge\, Matthew E. Kroeker\, and Peter Nelson.
URL:https://dimag.ibs.re.kr/event/2025-08-05/
LOCATION:Room B332\, IBS (기초과학연구원)
CATEGORIES:Discrete Math Seminar
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Asia/Seoul:20250812T163000
DTEND;TZID=Asia/Seoul:20250812T173000
DTSTAMP:20260416T025034
CREATED:20250702T055012Z
LAST-MODIFIED:20250702T055027Z
UID:11088-1755016200-1755019800@dimag.ibs.re.kr
SUMMARY:Chien-Chung Huang\, Robust Sparsification for Matroid Intersection with Applications
DESCRIPTION:The matroid intersection problem is a fundamental problem in combinatorial optimization. In this problem we are given two matroids and the goal is to find the largest common independent set in both matroids. This problem was introduced and solved by Edmonds in the 70s. The importance of matroid intersection stems from the large variety of combinatorial optimization problems it captures; well-known examples in computer science include bipartite matching and packing of spanning trees/arborescences. \nIn this talk\, we introduce a “sparsifer” for the matroid intersection problem and use it to design algorithms for two problems closely related to streaming: a one-way communication protocol and a streaming algorithm in the random-order streaming model. \nThis is a joint-work with François Sellier.
URL:https://dimag.ibs.re.kr/event/2025-08-12/
LOCATION:Room B332\, IBS (기초과학연구원)
CATEGORIES:Discrete Math Seminar
END:VEVENT
BEGIN:VEVENT
DTSTART;VALUE=DATE:20250818
DTEND;VALUE=DATE:20250821
DTSTAMP:20260416T025034
CREATED:20250322T120039Z
LAST-MODIFIED:20250818T042052Z
UID:10706-1755475200-1755734399@dimag.ibs.re.kr
SUMMARY:2025 Combinatorics Workshop (2025 조합론 학술대회)
DESCRIPTION:Website: https://cw2025.combinatorics.kr \nInvited Speakers\n\nDongsu Kim (KAIST)\nEun Jung Kim (KAIST)\nO-joung Kwon (Hanyang University)\nAe Ja Lee (Pennsylvania State University)\nZhicong Lin (Shandong University)\n\nOrganizing Committee\n\nSang-il Oum (엄상일)\, IBS Discrete Mathematics Group\nJang Soo Kim (김장수)\, Sungkyunkwan University\nSeunghyun Seo (서승현)\, Kangwon National University
URL:https://dimag.ibs.re.kr/event/cw2025/
LOCATION:IBS Science Culture Center
CATEGORIES:Workshops and Conferences
END:VEVENT
BEGIN:VEVENT
DTSTART;VALUE=DATE:20250820
DTEND;VALUE=DATE:20250825
DTSTAMP:20260416T025034
CREATED:20250722T052942Z
LAST-MODIFIED:20250722T053013Z
UID:11276-1755648000-1756079999@dimag.ibs.re.kr
SUMMARY:2025 Korean Student Combinatorics Workshop (KSCW2025: 2025 조합론 학생 워크샵)
DESCRIPTION:Venue\nThe K-Hotel Gyeongju \nWebsite\nhttps://indico.ibs.re.kr/e/kscw2025 \nOrganizers\n\nSeokbeom Kim (김석범)\, KAIST and IBS Discrete Mathematics Group\nHyunwoo Lee (이현우)\, KAIST and IBS Extremal Combinatorics and Probability Group\nJaehyeon Seo (서재현)\, Yonsei University\nKyungjin Cho (조경진)\, POSTECH
URL:https://dimag.ibs.re.kr/event/kscw2025/
LOCATION:The K-Hotel Gyeongju
CATEGORIES:Workshops and Conferences
END:VEVENT
END:VCALENDAR