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BEGIN:VEVENT
SUMMARY:David Wood (Monash University)
DTSTART:20200608T020000Z
DTEND:20200608T030000Z
DTSTAMP:20260421T084244Z
UID:RelayCombinatorics/1
DESCRIPTION:Title: <a href="https://researchseminars.org/talk/RelayCombina
 torics/1/">Universality in Minor-Closed Graph Classes</a>\nby David Wood (
 Monash University) as part of Round the world relay in combinatorics\n\n\n
 Abstract\nStanislaw Ulam asked whether there exists a universal countable 
 planar graph (that is\, a countable planar graph that contains every count
 able planar graph as a subgraph). János Pach (1981) answered this questio
 n in the negative. We strengthen this result by showing that every countab
 le graph that contains all countable planar graphs must contain an infinit
 e complete graph as a minor. On the other hand\, we construct a countable 
 graph that contains all countable planar graphs and has several key proper
 ties such as linear colouring numbers\, linear expansion\, and every finit
 e n-vertex subgraph has O(\\sqrt{n}) treewidth (which implies the Lipton-T
 arjan separator theorem). More generally\, for every fixed positive intege
 r t we construct a countable graph that contains every countable Kt-minor-
 free graph and has the above key properties. Joint work with Tony Huynh\, 
 Bojan Mohar\, Robert Samal and Carsten Thomassen.\n\nThis talk is organize
 d by the <a href="https://blogs.monash.edu/discretemaths/">Monash Discrete
  Mathematics Seminar</a>.\n
LOCATION:https://researchseminars.org/talk/RelayCombinatorics/1/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Baogang Xu (Nanjing Normal University)
DTSTART:20200608T030000Z
DTEND:20200608T040000Z
DTSTAMP:20260421T084244Z
UID:RelayCombinatorics/2
DESCRIPTION:Title: <a href="https://researchseminars.org/talk/RelayCombina
 torics/2/">On coloring of graphs of girth 2l+1 without longer odd holes</a
 >\nby Baogang Xu (Nanjing Normal University) as part of Round the world re
 lay in combinatorics\n\n\nAbstract\nA hole is an induced cycle of length a
 t least 4. Let l≥2 be a positive integer\, let Ĝl denote the family of 
 graphs which have girth 2l+1 and have no holes of odd length at least 2l+3
 \, and let G ∈ Ĝl. For a vertex u ∈ V(G) and a nonempty set S ⊆ V(G
 )\, let d(u\,S) = min{d(u\,v) : v∈S}\, and let Li(S)={u∈V(G) and d(u\,
 S)=i} for any integer i≥0. We show that if G[S] is connected and G[Li(S)
 ] is bipartite for each i∈{1…\,l-1}\, then G[Li(S)] is bipartite for e
 ach i>0\, and consequently χ(G)≤4\, where G[S] denotes the subgraph ind
 uced by S. For a graph G∈ Ĝ2\, we show that χ(G)≤3 if G induces no t
 wo cycles of length 5 sharing edges. Let θ+ be the graph obtained from th
 e Petersen graph by removing two adjacent vertices. We show that if G ∈ 
 Ĝ2 is 3-connected and has no unstable 3-cutset\, then G does not induce 
 θ+. As a corollary\, minimal non-3-colorable graphs of Ĝ2 induce no θ+.
  This is a joint work with Di Wu and Yian Xu.\n\nOrganized by the <a href=
 "https://scmscomb.github.io/">SCMS Combinatorics Seminar</a>.\n
LOCATION:https://researchseminars.org/talk/RelayCombinatorics/2/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Jeroen Schillewaert (University of Auckland)
DTSTART:20200608T040000Z
DTEND:20200608T050000Z
DTSTAMP:20260421T084244Z
UID:RelayCombinatorics/3
DESCRIPTION:Title: <a href="https://researchseminars.org/talk/RelayCombina
 torics/3/">Constructing highly regular expanders from hyperbolic Coxeter g
 roups</a>\nby Jeroen Schillewaert (University of Auckland) as part of Roun
 d the world relay in combinatorics\n\n\nAbstract\nGiven a string Coxeter s
 ystem (W\,S)\, we construct highly regular quotients of the 1-skeleton of 
 its universal polytope P\, which form an infinite family of expander graph
 s when (W\,S) is indefinite and P has finite vertex links. The regularity 
 of the graphs in this family depends on the Coxeter diagram of (W\,S). The
  expansion stems from superapproximation applied to (W\,S). This construct
 ion is also extended to cover Wythoffian polytopes. As a direct applicatio
 n\, we obtain several notable families of expander graphs with high levels
  of regularity\, answering\, in particular\, the question posed by Chapman
 \, Linial\, and Peled positively.\n(Joint work with Marston Conder\, Alexa
 nder Lubotzky and Francois Thilmany)\n\nThis talk is organized by the <a h
 ref="https://www.math.auckland.ac.nz/en/about/news-and-events/seminars.htm
 l">Algebra and Combinatorics seminar</a> at the University of Auckland\, N
 ew Zealand.\n
LOCATION:https://researchseminars.org/talk/RelayCombinatorics/3/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Gordon Royle (University of Western Australia)
DTSTART:20200608T050000Z
DTEND:20200608T060000Z
DTSTAMP:20260421T084244Z
UID:RelayCombinatorics/4
DESCRIPTION:Title: <a href="https://researchseminars.org/talk/RelayCombina
 torics/4/">Real chromatic roots of planar graphs (CMSA seminar)</a>\nby Go
 rdon Royle (University of Western Australia) as part of Round the world re
 lay in combinatorics\n\n\nAbstract\nThe chromatic polynomial P(G\,q) of a 
 graph G is the function that\, for positive integer q\, counts the number 
 of proper q-colourings of the graph. The resulting function is a polynomia
 l so\, whether or not it makes any combinatorial sense\, we can evaluate i
 t at any complex number and therefore find its roots which may be integer\
 , real of complex. The overall aim of this heavily studied topic is to und
 erstand the relationship between the properties of a graph and the locatio
 n of its chromatic roots.\n\nIn this talk\, I will focus on the real roots
  of the chromatic polynomials of planar graphs. I will start by giving som
 e of the history\, background and basic results\, before focussing on effo
 rts (by myself and others) to show that planar chromatic roots are dense i
 n the real interval (3\,4).\nThe talk is mostly at a general level and any
 one familiar with the basic concepts of graphs\, proper colourings of grap
 hs and polynomials will be able to follow the gist of it.\n\nThis talk is 
 organized by the <a href="http://combinatorics-australasia.org/seminars.ht
 ml">CMSA seminar</a>.\n
LOCATION:https://researchseminars.org/talk/RelayCombinatorics/4/
END:VEVENT
BEGIN:VEVENT
SUMMARY:O-joung Kwon (Incheon National University and IBS Discrete Mathema
 tics Group)
DTSTART:20200608T060000Z
DTEND:20200608T070000Z
DTSTAMP:20260421T084244Z
UID:RelayCombinatorics/5
DESCRIPTION:Title: <a href="https://researchseminars.org/talk/RelayCombina
 torics/5/">Classes of intersection digraphs with good algorithmic properti
 es</a>\nby O-joung Kwon (Incheon National University and IBS Discrete Math
 ematics Group) as part of Round the world relay in combinatorics\n\nAbstra
 ct: TBA\n\nThis talk is organized by the <a href="https://dimag.ibs.re.kr/
 events/category/seminar/dms/">Discrete Math Seminar</a> at the IBS Discret
 e Mathematics Group.\n
LOCATION:https://researchseminars.org/talk/RelayCombinatorics/5/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Bartosz Walczak (Jagiellonian University)
DTSTART:20200608T070000Z
DTEND:20200608T080000Z
DTSTAMP:20260421T084244Z
UID:RelayCombinatorics/6
DESCRIPTION:Title: <a href="https://researchseminars.org/talk/RelayCombina
 torics/6/">Coloring polygon visibility graphs and their generalizations</a
 >\nby Bartosz Walczak (Jagiellonian University) as part of Round the world
  relay in combinatorics\n\n\nAbstract\nThe visibility graph of a polygon P
  is formed by the pairs of vertices u and v of P such that the segment uv 
 is disjoint from the exterior of P. We show that the class of polygon visi
 bility graphs is χ-bounded\, thus answering a question by Kára\, Pór\, 
 and Wood from 2005. Specifically\, we prove the bound χ≤3·4ω-1. We ob
 tain the same bound for generalizations of polygon visibility graphs in wh
 ich the polygon is replaced by a curve and straight-line segments are repl
 aced by segments in a pseudo-line arrangement. The proof is carried throug
 h in the setting of ordered graphs. In particular\, we show χ-boundedness
  of several classes of ordered graphs with excluded ordered substructures.
  Joint work with James Davies\, Tomasz Krawczyk\, and Rose McCarty.\n\nThi
 s talk is organized by the <a href="https://www.tcs.uj.edu.pl/informatyka-
 teoretyczna">TCS Seminar</a> at the Jagiellonian University.\n
LOCATION:https://researchseminars.org/talk/RelayCombinatorics/6/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Heng Guo (University of Edinburgh)
DTSTART:20200608T080000Z
DTEND:20200608T090000Z
DTSTAMP:20260421T084244Z
UID:RelayCombinatorics/7
DESCRIPTION:Title: <a href="https://researchseminars.org/talk/RelayCombina
 torics/7/">A Markov chain approach towards the sampling Lovász local lemm
 a</a>\nby Heng Guo (University of Edinburgh) as part of Round the world re
 lay in combinatorics\n\n\nAbstract\nLovász local lemma is a powerful tool
  to establish the existence of combinatorial objects under certain depende
 ncy conditions. The algorithmic local lemma by Moser and Tardos gives an e
 fficient way to find such objects. We are interested in the sampling local
  lemma\, whose goal is to uniformly generate these objects efficiently\, p
 otentially under stronger conditions than those of the local lemma. This s
 ampling problem has seen some rapid advances in recent years\, and in this
  talk I will illustrate a Markov chain approach for this task. The running
  example will be sampling solutions to k-CNF formulas where each variable 
 does not appear in too many clauses. The main difficulty to design a Marko
 v chain here is that the solution space is not connected via local moves. 
 This issue will be circumvented by a projection idea.\n\nThis talk is orga
 nized by the Mini Online Scottish Combinatorics Meeting.\n
LOCATION:https://researchseminars.org/talk/RelayCombinatorics/7/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Annika Heckel (LMU)
DTSTART:20200608T090000Z
DTEND:20200608T100000Z
DTSTAMP:20260421T084244Z
UID:RelayCombinatorics/8
DESCRIPTION:Title: <a href="https://researchseminars.org/talk/RelayCombina
 torics/8/">How does the chromatic number of a random graph vary?</a>\nby A
 nnika Heckel (LMU) as part of Round the world relay in combinatorics\n\n\n
 Abstract\nHow much does the chromatic number of the random graph G(n\, 1/2
 ) vary? Shamir and Spencer proved that it is contained in some sequence of
  intervals of length about $n^{1/2}$. Alon improved this slightly to $n^{1
 /2} / \\log n$. Until recently\, however\, no lower bounds on the fluctuat
 ions of the chromatic number of G(n\, 1/2) were known\, even though the qu
 estion was raised by Bollobás many years ago. I will talk about the main 
 ideas needed to prove that\, at least for infinitely many n\, the chromati
 c number of G(n\, 1/2) is not concentrated on fewer than $n^{1/2-o(1)}$ co
 nsecutive values.\nI will also discuss the Zigzag Conjecture\, made recent
 ly by Bollobás\, Heckel\, Morris\, Panagiotou\, Riordan and Smith: this p
 roposes that the correct concentration interval length 'zigzags' between $
 n^{1/4+o(1)}$ and $n^{1/2+o(1)}$\, depending on n.\nJoint work with Oliver
  Riordan.\n\nOrganized by the <a href="https://www.lse.ac.uk/Mathematics/E
 vents-and-Seminars/Seminar-and-PhD-Seminar-on-Combinatorics-Games-and-Opti
 misation">Seminar on Combinatorics\, Games and Optimisation</a> at London 
 School of Economics.\n
LOCATION:https://researchseminars.org/talk/RelayCombinatorics/8/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Noga Alon (Princeton University and Tel Aviv University)
DTSTART:20200608T100000Z
DTEND:20200608T110000Z
DTSTAMP:20260421T084244Z
UID:RelayCombinatorics/9
DESCRIPTION:Title: <a href="https://researchseminars.org/talk/RelayCombina
 torics/9/">Splitting Random Necklaces</a>\nby Noga Alon (Princeton Univers
 ity and Tel Aviv University) as part of Round the world relay in combinato
 rics\n\n\nAbstract\nLet N be a random necklace with km beads of each of t 
 types. What is the typical minimum number of points in which one can cut N
  so that it will be possible to partition the resulting intervals of beads
  into k collections\, each containing exactly m beads of each type ? It is
  known that this number is at most (k-1)t with probability 1\, is it typic
 ally significantly smaller? I will discuss a recent joint work with Dor El
 boim\, Janos Pach and Gabor Tardos addressing this problem and showing tha
 t it is connected to several seemingly unrelated topics\, including matchi
 ngs in nearly regular hypergraphs and random walks in Euclidean spaces.\n\
 nOrganized by <a href="https://combgeo.org/en/events/big-seminar/">MIPT Bi
 g Seminar of Combinatorics and Geometry</a>.\n
LOCATION:https://researchseminars.org/talk/RelayCombinatorics/9/
END:VEVENT
BEGIN:VEVENT
SUMMARY:László Lovász (Eotvos University)
DTSTART:20200608T110000Z
DTEND:20200608T120000Z
DTSTAMP:20260421T084244Z
UID:RelayCombinatorics/10
DESCRIPTION:Title: <a href="https://researchseminars.org/talk/RelayCombina
 torics/10/">Orthogonal representations and graph limits</a>\nby László L
 ovász (Eotvos University) as part of Round the world relay in combinatori
 cs\n\n\nAbstract\nOrthogonal representations have played a role in informa
 tion theory\, combinatorial optimization\, rigidity theory and quantum phy
 sics. We start with a survey of these connections.\n\nRecent interest in t
 his construction is motivated by graph limit theory. Limit objects of conv
 ergent graph sequences have been defined in the two extreme cases: graphon
 s (limits of dense graph sequences) and graphings (limits of bounded-degre
 e graph sequences). In the middle ranges\, Markov chains seem to play an i
 mportant role. An interesting example from this point of view is the Marko
 v chain on the sphere in a fixed dimension\, where a step is a move by 90 
 degrees in any direction.\n\nA basic question: is this object a limit of f
 inite graphs (and in what sense)? To get an affirmative answer\, we need t
 o define the density of a given simple graph in the orthogonality graph. T
 his leads to the problem of defining and computing a random orthogonal rep
 resentation of this graph\, which is an interesting and nontrivial issue o
 n its own.\n\nOrganized by the <a href="https://coge.elte.hu/seminar.html"
 >Budapest (BBC+G) seminar</a>.\n
LOCATION:https://researchseminars.org/talk/RelayCombinatorics/10/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Carla Groenland (Utrecht University)
DTSTART:20200608T120000Z
DTEND:20200608T130000Z
DTSTAMP:20260421T084244Z
UID:RelayCombinatorics/11
DESCRIPTION:Title: <a href="https://researchseminars.org/talk/RelayCombina
 torics/11/">Universal Graphs and Labelling Schemes</a>\nby Carla Groenland
  (Utrecht University) as part of Round the world relay in combinatorics\n\
 n\nAbstract\nAn induced universal graph for a graph class contains all gra
 phs in the class as an induced subgraph. We construct induced universal gr
 aphs for all hereditary graph classes\, and derive reachability labelling 
 schemes for digraphs and comparability labelling schemes for posets from t
 his. All these results are asymptotically optimal. This talk aims to give 
 some intuition about these concepts and our techniques (including Szemered
 i regularity lemma and efficient dictionaries). We will also discuss a new
  venue of research: what if we strengthen induced to isometric? Several in
 teresting questions are left open.\nThis is based on joint work with Marth
 e Bonamy\, Louis Esperet\, Cyril Gavoille and Alex Scott.\n\nThis talk is 
 organized by <a href="https://graphesetoptimisation.labri.fr/pmwiki.php/Gr
 oupe/GT">Bordeaux Seminar</a>.\n
LOCATION:https://researchseminars.org/talk/RelayCombinatorics/11/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Deepak Bal (Montclair State University)
DTSTART:20200608T130000Z
DTEND:20200608T140000Z
DTSTAMP:20260421T084244Z
UID:RelayCombinatorics/12
DESCRIPTION:Title: <a href="https://researchseminars.org/talk/RelayCombina
 torics/12/">Size Ramsey numbers of paths and cycles</a>\nby Deepak Bal (Mo
 ntclair State University) as part of Round the world relay in combinatoric
 s\n\n\nAbstract\nLet $\\mathcal F_1$ and $\\mathcal F_2$ be two families o
 f graphs. The size Ramsey number $\\hat{R}(\\mathcal F_1\, \\mathcal F_2)$
  is the smallest number $m$ such that there exists a graph $G$ with $m$ ed
 ges in which every red-blue coloring of $E(G)$ contains either a red graph
  from $\\mathcal F_1$ or a blue graph from $\\mathcal F_1$. Let $P_n$ repr
 esent the path on $n$ vertices and let $\\mathcal C$ represent the family 
 of all cycles. We discuss some recent progress on size Ramsey numbers in t
 he cases where $\\mathcal F_1 = \\mathcal F_2 = \\{P_n\\}$ (improvement of
  lower bound) and where $\\mathcal F_1 = \\{P_n\\}$\, $\\mathcal F_2 = \\m
 athcal C$ (improvement of lower and upper bounds). We will also discuss so
 me recent results concerning the size Ramsey number of hypergraph paths. T
 his is based on joint works with DeBiasio and Schudrich.\n\nThis talk is o
 rganized by the <a href="http://userhome.brooklyn.cuny.edu/skingan/Combina
 toricsSeminar/">NYC Combinatorics Seminar</a>.\n
LOCATION:https://researchseminars.org/talk/RelayCombinatorics/12/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Dhruv Mubayi (University of Illinois at Chicago)
DTSTART:20200608T140000Z
DTEND:20200608T150000Z
DTSTAMP:20260421T084244Z
UID:RelayCombinatorics/13
DESCRIPTION:Title: <a href="https://researchseminars.org/talk/RelayCombina
 torics/13/">The feasible region of hypergraphs</a>\nby Dhruv Mubayi (Unive
 rsity of Illinois at Chicago) as part of Round the world relay in combinat
 orics\n\n\nAbstract\nMany extremal hypergraph problems seek to maximize th
 e number of edges subject to some local constraints. We aim to gain a more
  detailed understanding of such problems by studying the maximum subject t
 o an additional global constraint\, namely the size of the shadow. Put dif
 ferently\, we seek the pairs (x\,y) in the unit square such that there are
  F-free hypergraphs whose shadow density approaches x and edge density app
 roaches y. I will give some general results about the shape of this "feasi
 ble region" and also extend and improve some classical Turan-type results 
 for particular choices of F. This is joint work with Xizhi Liu.\n\nThis ta
 lk is organized by the <a href="https://sites.google.com/view/epcwebinar/"
 >Extremal and Probabilistic Combinatorics Webinar</a>.\n
LOCATION:https://researchseminars.org/talk/RelayCombinatorics/13/
END:VEVENT
BEGIN:VEVENT
SUMMARY:James Davies (University of Waterloo)
DTSTART:20200608T150000Z
DTEND:20200608T160000Z
DTSTAMP:20260421T084244Z
UID:RelayCombinatorics/14
DESCRIPTION:Title: <a href="https://researchseminars.org/talk/RelayCombina
 torics/14/">Colouring circle graphs and their generalisations</a>\nby Jame
 s Davies (University of Waterloo) as part of Round the world relay in comb
 inatorics\n\n\nAbstract\nA circle graph is an intersection graph of a set 
 of chords on a circle\; vertices are adjacent whenever their corresponding
  chords intersect. A classical graph colouring result due to Gyárfás sta
 tes that circle graphs are $\\chi$-bounded\, i.e.\, circle graphs with bou
 nded clique number have bounded chromatic number. I will discuss some rece
 nt results concerning $\\chi$-boundedness of circle graphs and various mor
 e general classes that contain them.\n\nThis talk includes joint work with
  Tomasz Krawczyk\, Rose McCarty\, and Bartosz Walczak.\n\nThis talk is org
 anized by the <https://www.fi.muni.cz/dfseminar/index.html.en>Joint DIMEA 
 and FORMELA seminar</a> at Masaryk University.\n
LOCATION:https://researchseminars.org/talk/RelayCombinatorics/14/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Jacob Fox (Stanford University)
DTSTART:20200608T160000Z
DTEND:20200608T170000Z
DTSTAMP:20260421T084244Z
UID:RelayCombinatorics/15
DESCRIPTION:Title: <a href="https://researchseminars.org/talk/RelayCombina
 torics/15/">Removal lemmas</a>\nby Jacob Fox (Stanford University) as part
  of Round the world relay in combinatorics\n\n\nAbstract\nThe triangle rem
 oval lemma is a central result in extremal combinatorics\, with many appli
 cations in number theory\, graph theory\, discrete geometry\, and theoreti
 cal computer science. It says that any graph with n vertices and $o(n^3)$ 
 triangles can be made triangle-free by removing $o(n^2)$ edges. In this ta
 lk\, I will survey recent extensions and variants\, quantitative aspects\,
  applications\, and open problems.\n\nThis talk is organized by the <a hre
 f="https://people.maths.ox.ac.uk/scott/dmp.htm">Oxford Discrete Mathematic
 s and Probability Seminar</a>.\n
LOCATION:https://researchseminars.org/talk/RelayCombinatorics/15/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Allan Sly (Princeton University)
DTSTART:20200608T170000Z
DTEND:20200608T180000Z
DTSTAMP:20260421T084244Z
UID:RelayCombinatorics/16
DESCRIPTION:Title: <a href="https://researchseminars.org/talk/RelayCombina
 torics/16/">Spread of infections in random walkers</a>\nby Allan Sly (Prin
 ceton University) as part of Round the world relay in combinatorics\n\n\nA
 bstract\nWe consider a class of interacting particle systems where particl
 es perform independent random walks on Zd and spread an infection accordin
 g to a Susceptible-Infectious-Recovered or SIR model. We show that if the 
 recovery rate is low enough\, the infection spreads linearly. I will descr
 ibe new methods to understand growth processes in such models.\n\nJoint wo
 rk with Duncan Dauvergne.\n\nThis talk is organized by <a href="https://u.
 osu.edu/probability/">The Ohio State University Combinatorics & Probabilit
 y Seminar</a>.\n
LOCATION:https://researchseminars.org/talk/RelayCombinatorics/16/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Marcelo Campos (IMPA)
DTSTART:20200608T180000Z
DTEND:20200608T190000Z
DTSTAMP:20260421T084244Z
UID:RelayCombinatorics/17
DESCRIPTION:Title: <a href="https://researchseminars.org/talk/RelayCombina
 torics/17/">The singularity probability of a random symmetric matrix is ex
 ponentially small</a>\nby Marcelo Campos (IMPA) as part of Round the world
  relay in combinatorics\n\n\nAbstract\nLet A be drawn uniformly at random 
 from the set of all n x n symmetric matrices with entries in {-1\,1}. I'll
  describe some recent work where we show that Pr(det(A) = 0) < e-cn for so
 me absolute constant c > 0.\n\nJoint work with Matthew Jenssen\, Marcus Mi
 chelen and Julian Sahasrabudhe.\n
LOCATION:https://researchseminars.org/talk/RelayCombinatorics/17/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Jim Geelen (University of Waterloo)
DTSTART:20200608T190000Z
DTEND:20200608T200000Z
DTSTAMP:20260421T084244Z
UID:RelayCombinatorics/18
DESCRIPTION:Title: <a href="https://researchseminars.org/talk/RelayCombina
 torics/18/">Homomorphisms and colouring for graphs and binary matroids</a>
 \nby Jim Geelen (University of Waterloo) as part of Round the world relay 
 in combinatorics\n\n\nAbstract\nThe talk starts with Rödl's Theorem that 
 graphs with huge chromatic number contain triangle-free subgraphs with lar
 ge chromatic number. We will look at various related results and conjectur
 es\, with a notable matroid bias\; the new results are joint work with Pet
 er Nelson and Raphael Steiner.\n\nOrganized by the <a href="https://people
 .math.gatech.edu/~abernshteyn3/gt_gt/">Georgia Tech Graph Theory Seminar</
 a>.\n
LOCATION:https://researchseminars.org/talk/RelayCombinatorics/18/
END:VEVENT
BEGIN:VEVENT
SUMMARY:David Conlon (Caltech)
DTSTART:20200608T200000Z
DTEND:20200608T210000Z
DTSTAMP:20260421T084244Z
UID:RelayCombinatorics/19
DESCRIPTION:Title: <a href="https://researchseminars.org/talk/RelayCombina
 torics/19/">Random multilinear maps and the Erdős box problem</a>\nby Dav
 id Conlon (Caltech) as part of Round the world relay in combinatorics\n\n\
 nAbstract\nBy using random multilinear maps\, we provide new lower bounds 
 for the Erdős box problem\, the problem of estimating the extremal number
  of the complete d-partite d-uniform hypergraph with two vertices in each 
 part\, thereby improving on work of Gunderson\, Rödl and Sidorenko. Joint
  work with Cosmin Pohoata and Dmitriy Zakharov.\n\nOrganized by the <a hre
 f="https://sites.google.com/view/agco-seminar-chile/home">AGCO Seminar</a>
 \, Chile.\n
LOCATION:https://researchseminars.org/talk/RelayCombinatorics/19/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Fan Chung (UCSD)
DTSTART:20200608T210000Z
DTEND:20200608T220000Z
DTSTAMP:20260421T084244Z
UID:RelayCombinatorics/20
DESCRIPTION:Title: <a href="https://researchseminars.org/talk/RelayCombina
 torics/20/">Trees and forests in Green's functions of a graph</a>\nby Fan 
 Chung (UCSD) as part of Round the world relay in combinatorics\n\n\nAbstra
 ct\nThe Green's functions of a graph are the pseudo inverses of the Laplac
 ians and therefore are useful for solving many types of Laplace equations 
 in discrete settings.\nIn this talk\, we will give combinatorial interpret
 ations of Green's functions in terms of Counting trees and forests in a gr
 aph. We will also mention several applications concerning the pagerank alg
 orithms and the hitting time for random walks.\n\nOrganized by the <a href
 ="https://www.sfu.ca/math/research/discrete-mathematics/discrete-math-semi
 nars.html">SFU Discrete Math Seminar</a>.\n
LOCATION:https://researchseminars.org/talk/RelayCombinatorics/20/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Andrew Suk (UCSD)
DTSTART:20200608T220000Z
DTEND:20200608T230000Z
DTSTAMP:20260421T084244Z
UID:RelayCombinatorics/21
DESCRIPTION:Title: <a href="https://researchseminars.org/talk/RelayCombina
 torics/21/">Turán-type problems for point-line incidences</a>\nby Andrew 
 Suk (UCSD) as part of Round the world relay in combinatorics\n\n\nAbstract
 \nIn this talk\, I will discuss several Turán-type results for point-line
  incidences. It will be based on joint works with Istvan Tomon and Mozhgan
  Mirzaei.\n\nOrganized by the <a href="https://www.uvic.ca/science/math-st
 atistics/home/home/events/seminars/discrete-math/index.php">University of 
 Victoria Discrete Math Seminar</a>.\n
LOCATION:https://researchseminars.org/talk/RelayCombinatorics/21/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Ron Gould (Emory)
DTSTART:20200608T230000Z
DTEND:20200608T235900Z
DTSTAMP:20260421T084244Z
UID:RelayCombinatorics/22
DESCRIPTION:Title: <a href="https://researchseminars.org/talk/RelayCombina
 torics/22/">Chorded cycles</a>\nby Ron Gould (Emory) as part of Round the 
 world relay in combinatorics\n\n\nAbstract\nA chord of a cycle is an edge 
 between two vertices of the cycle that is not an edge of the cycle. A cycl
 e in a graph G is said to be chorded if its vertices induce at least one c
 hord\, and it is called doubly chorded if its vertices induce two or more 
 chords. The past decade has seen a vast increase in the study of chorded c
 ycles.\n\nIn this talk I will survey a variety of results dealing with cho
 rded cycles. I will consider several types of questions dealing with chord
 ed cycles and con- sider the major known results in each of these areas. T
 his includes minimum degree and degree sum results\, forbidden subgraph re
 sults\, and edge density results. We will ask questions like:` When can an
  edge be a chord of a cycle and when can an edge be a cycle edge of a chor
 ded cycle? Many times\, I will try to place these chorded cycle results in
  relation to known results on cycles and show that the chorded cycle resul
 ts are actually natural extensions of known cycle results.\n\nOrganized by
  the University of Alaska Fairbanks Seminar.\n
LOCATION:https://researchseminars.org/talk/RelayCombinatorics/22/
END:VEVENT
BEGIN:VEVENT
SUMMARY:David Wood (Monash University)
DTSTART:20210608T020000Z
DTEND:20210608T030000Z
DTSTAMP:20260421T084244Z
UID:RelayCombinatorics/23
DESCRIPTION:Title: <a href="https://researchseminars.org/talk/RelayCombina
 torics/23/">Universality in Minor-Closed Graph Classes</a>\nby David Wood 
 (Monash University) as part of Round the world relay in combinatorics\n\n\
 nAbstract\nStanislaw Ulam asked whether there exists a universal countable
  planar graph (that is\, a countable planar graph that contains every coun
 table planar graph as a subgraph). János Pach (1981) answered this questi
 on in the negative. We strengthen this result by showing that every counta
 ble graph that contains all countable planar graphs must contain an infini
 te complete graph as a minor. On the other hand\, we construct a countable
  graph that contains all countable planar graphs and has several key prope
 rties such as linear colouring numbers\, linear expansion\, and every fini
 te n-vertex subgraph has O(\\sqrt{n}) treewidth (which implies the Lipton-
 Tarjan separator theorem). More generally\, for every fixed positive integ
 er t we construct a countable graph that contains every countable Kt-minor
 -free graph and has the above key properties. Joint work with Tony Huynh\,
  Bojan Mohar\, Robert Samal and Carsten Thomassen.\n\nOrganized by the <a 
 href="https://blogs.monash.edu/discretemaths/">Monash Discrete Mathematics
  Seminar</a>.\n
LOCATION:https://researchseminars.org/talk/RelayCombinatorics/23/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Baogang Xu (Nanjing Normal University)
DTSTART:20210608T030000Z
DTEND:20210608T040000Z
DTSTAMP:20260421T084244Z
UID:RelayCombinatorics/24
DESCRIPTION:Title: <a href="https://researchseminars.org/talk/RelayCombina
 torics/24/">On coloring of graphs of girth 2l+1 without longer odd holes</
 a>\nby Baogang Xu (Nanjing Normal University) as part of Round the world r
 elay in combinatorics\n\n\nAbstract\nA hole is an induced cycle of length 
 at least 4. Let l≥2 be a positive integer\, let Ĝl denote the family of
  graphs which have girth 2l+1 and have no holes of odd length at least 2l+
 3\, and let G ∈ Ĝl. For a vertex u ∈ V(G) and a nonempty set S ⊆ V(
 G)\, let d(u\,S) = min{d(u\,v) : v∈S}\, and let Li(S)={u∈V(G) and d(u\
 ,S)=i} for any integer i≥0. We show that if G[S] is connected and G[Li(S
 )] is bipartite for each i∈{1…\,l-1}\, then G[Li(S)] is bipartite for 
 each i>0\, and consequently χ(G)≤4\, where G[S] denotes the subgraph in
 duced by S. For a graph G∈ Ĝ2\, we show that χ(G)≤3 if G induces no 
 two cycles of length 5 sharing edges. Let θ+ be the graph obtained from t
 he Petersen graph by removing two adjacent vertices. We show that if G ∈
  Ĝ2 is 3-connected and has no unstable 3-cutset\, then G does not induce 
 θ+. As a corollary\, minimal non-3-colorable graphs of Ĝ2 induce no θ+.
  This is a joint work with Di Wu and Yian Xu.\n\nOrganized by the <a href=
 "https://scmscomb.github.io/">SCMS Combinatorics Seminar</a>.\n
LOCATION:https://researchseminars.org/talk/RelayCombinatorics/24/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Jeroen Schillewaert (University of Auckland)
DTSTART:20210608T040000Z
DTEND:20210608T050000Z
DTSTAMP:20260421T084244Z
UID:RelayCombinatorics/25
DESCRIPTION:Title: <a href="https://researchseminars.org/talk/RelayCombina
 torics/25/">Constructing highly regular expanders from hyperbolic Coxeter 
 groups</a>\nby Jeroen Schillewaert (University of Auckland) as part of Rou
 nd the world relay in combinatorics\n\n\nAbstract\nGiven a string Coxeter 
 system (W\,S)\, we construct highly regular quotients of the 1-skeleton of
  its universal polytope P\, which form an infinite family of expander grap
 hs when (W\,S) is indefinite and P has finite vertex links. The regularity
  of the graphs in this family depends on the Coxeter diagram of (W\,S). Th
 e expansion stems from superapproximation applied to (W\,S). This construc
 tion is also extended to cover Wythoffian polytopes. As a direct applicati
 on\, we obtain several notable families of expander graphs with high level
 s of regularity\, answering\, in particular\, the question posed by Chapma
 n\, Linial\, and Peled positively.\n(Joint work with Marston Conder\, Alex
 ander Lubotzky and Francois Thilmany)\n\nOrganized by the  <a href="https:
 //www.math.auckland.ac.nz/en/about/news-and-events/seminars.html">Algebra 
 and Combinatorics seminar</a> of the University of Auckland.\n
LOCATION:https://researchseminars.org/talk/RelayCombinatorics/25/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Gordon Royle (University of Western Australia)
DTSTART:20210608T050000Z
DTEND:20210608T060000Z
DTSTAMP:20260421T084244Z
UID:RelayCombinatorics/26
DESCRIPTION:Title: <a href="https://researchseminars.org/talk/RelayCombina
 torics/26/">Real chromatic roots of planar graphs</a>\nby Gordon Royle (Un
 iversity of Western Australia) as part of Round the world relay in combina
 torics\n\n\nAbstract\nThe chromatic polynomial P(G\,q) of a graph G is the
  function that\, for positive integer q\, counts the number of proper q-co
 lourings of the graph. The resulting function is a polynomial so\, whether
  or not it makes any combinatorial sense\, we can evaluate it at any compl
 ex number and therefore find its roots which may be integer\, real of comp
 lex. The overall aim of this heavily studied topic is to understand the re
 lationship between the properties of a graph and the location of its chrom
 atic roots.\nIn this talk\, I will focus on the real roots of the chromati
 c polynomials of planar graphs. I will start by giving some of the history
 \, background and basic results\, before focussing on efforts (by myself a
 nd others) to show that planar chromatic roots are dense in the real inter
 val (3\,4).\nThe talk is mostly at a general level and anyone familiar wit
 h the basic concepts of graphs\, proper colourings of graphs and polynomia
 ls will be able to follow the gist of it.\n\nOrganized by the <a href="htt
 p://combinatorics-australasia.org/seminars.html">CMSA seminar</a>.\n
LOCATION:https://researchseminars.org/talk/RelayCombinatorics/26/
END:VEVENT
BEGIN:VEVENT
SUMMARY:O-joung Kwon (Incheon National University and IBS Discrete Mathema
 tics Group)
DTSTART:20210608T060000Z
DTEND:20210608T070000Z
DTSTAMP:20260421T084244Z
UID:RelayCombinatorics/27
DESCRIPTION:Title: <a href="https://researchseminars.org/talk/RelayCombina
 torics/27/">Classes of intersection digraphs with good algorithmic propert
 ies</a>\nby O-joung Kwon (Incheon National University and IBS Discrete Mat
 hematics Group) as part of Round the world relay in combinatorics\n\n\nAbs
 tract\nAn intersection digraph is a digraph where every vertex v is repres
 ented by an ordered pair (Sv\, Tv) of sets such that there is an edge from
  v to w if and only if Sv and Tw intersect. An intersection digraph is ref
 lexive if Sv∩ Tv≠ ∅ for every vertex v. Compared to well-known undir
 ected intersection graphs like interval graphs and permutation graphs\, no
 t many algorithmic applications on intersection digraphs have been develop
 ed.\nMotivated by the successful story on algorithmic applications of inte
 rsection graphs using a graph width parameter called mim-width\, we introd
 uce its directed analogue called `bi-mim-width' and prove that various cla
 sses of reflexive intersection digraphs have bounded bi-mim-width. In part
 icular\, we show that as a natural extension of H-graphs\, reflexive H-dig
 raphs have linear bi-mim-width at most 12|E(H)|\, which extends a bound on
  the linear mim-width of H-graphs [On the Tractability of Optimization Pro
 blems on H-Graphs. Algorithmica 2020].\nFor applications\, we introduce a 
 novel framework of directed versions of locally checkable problems\, that 
 streamlines the definitions and the study of many problems in the literatu
 re and facilitates their common algorithmic treatment. We obtain unified p
 olynomial-time algorithms for these problems on digraphs of bounded bi-mim
 -width\, when a branch decomposition is given. Locally checkable problems 
 include Kernel\, Dominating Set\, and Directed H-Homomorphism.\nThis is jo
 int work with Lars Jaffke and Jan Arne Telle.\n\nOrganized by the <a href=
 "https://dimag.ibs.re.kr/events/category/seminar/dms/">Discrete Math Semin
 ar</a> at the IBS Discrete Mathematics Group.\n
LOCATION:https://researchseminars.org/talk/RelayCombinatorics/27/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Bartosz Walczak (Jagiellonian University)
DTSTART:20210608T070000Z
DTEND:20210608T080000Z
DTSTAMP:20260421T084244Z
UID:RelayCombinatorics/28
DESCRIPTION:Title: <a href="https://researchseminars.org/talk/RelayCombina
 torics/28/">Coloring polygon visibility graphs and their generalizations</
 a>\nby Bartosz Walczak (Jagiellonian University) as part of Round the worl
 d relay in combinatorics\n\n\nAbstract\nThe visibility graph of a polygon 
 P is formed by the pairs of vertices u and v of P such that the segment uv
  is disjoint from the exterior of P. We show that the class of polygon vis
 ibility graphs is χ-bounded\, thus answering a question by Kára\, Pór\,
  and Wood from 2005. Specifically\, we prove the bound χ≤3·4ω-1. We o
 btain the same bound for generalizations of polygon visibility graphs in w
 hich the polygon is replaced by a curve and straight-line segments are rep
 laced by segments in a pseudo-line arrangement. The proof is carried throu
 gh in the setting of ordered graphs. In particular\, we show χ-boundednes
 s of several classes of ordered graphs with excluded ordered substructures
 . Joint work with James Davies\, Tomasz Krawczyk\, and Rose McCarty.\n\nOr
 ganized by the <a href="https://www.tcs.uj.edu.pl/informatyka-teoretyczna"
 >TCS Seminar at Jagiellonian University</a>.\n
LOCATION:https://researchseminars.org/talk/RelayCombinatorics/28/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Heng Guo (University of Edinburgh)
DTSTART:20210608T080000Z
DTEND:20210608T090000Z
DTSTAMP:20260421T084244Z
UID:RelayCombinatorics/29
DESCRIPTION:Title: <a href="https://researchseminars.org/talk/RelayCombina
 torics/29/">A Markov chain approach towards the sampling Lovász local lem
 ma</a>\nby Heng Guo (University of Edinburgh) as part of Round the world r
 elay in combinatorics\n\n\nAbstract\nLovász local lemma is a powerful too
 l to establish the existence of combinatorial objects under certain depend
 ency conditions. The algorithmic local lemma by Moser and Tardos gives an 
 efficient way to find such objects. We are interested in the sampling loca
 l lemma\, whose goal is to uniformly generate these objects efficiently\, 
 potentially under stronger conditions than those of the local lemma. This 
 sampling problem has seen some rapid advances in recent years\, and in thi
 s talk I will illustrate a Markov chain approach for this task. The runnin
 g example will be sampling solutions to k-CNF formulas where each variable
  does not appear in too many clauses. The main difficulty to design a Mark
 ov chain here is that the solution space is not connected via local moves.
  This issue will be circumvented by a projection idea.\n\nOrganized as the
  Mini Online Scottish Combinatorics Meeting by Kitty Meeks.\n
LOCATION:https://researchseminars.org/talk/RelayCombinatorics/29/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Annika Heckel (LMU)
DTSTART:20210608T090000Z
DTEND:20210608T100000Z
DTSTAMP:20260421T084244Z
UID:RelayCombinatorics/30
DESCRIPTION:Title: <a href="https://researchseminars.org/talk/RelayCombina
 torics/30/">How does the chromatic number of a random graph vary?</a>\nby 
 Annika Heckel (LMU) as part of Round the world relay in combinatorics\n\n\
 nAbstract\nHow much does the chromatic number of the random graph G(n\, 1/
 2) vary? Shamir and Spencer proved that it is contained in some sequence o
 f intervals of length about $n^{1/2}$. Alon improved this slightly to $n^{
 1/2} / \\log n$. Until recently\, however\, no lower bounds on the fluctua
 tions of the chromatic number of G(n\, 1/2) were known\, even though the q
 uestion was raised by Bollobás many years ago. I will talk about the main
  ideas needed to prove that\, at least for infinitely many n\, the chromat
 ic number of G(n\, 1/2) is not concentrated on fewer than $n^{1/2-o(1)}$ c
 onsecutive values.\nI will also discuss the Zigzag Conjecture\, made recen
 tly by Bollobás\, Heckel\, Morris\, Panagiotou\, Riordan and Smith: this 
 proposes that the correct concentration interval length 'zigzags' between 
 $n^{1/4+o(1)}$ and $n^{1/2+o(1)}$\, depending on n.\nJoint work with Olive
 r Riordan.\n\nOrganized by the <a href="https://www.lse.ac.uk/Mathematics/
 Events-and-Seminars/Seminar-and-PhD-Seminar-on-Combinatorics-Games-and-Opt
 imisation">Seminar on Combinatorics\, Games and Optimisation</a> at LSE.\n
LOCATION:https://researchseminars.org/talk/RelayCombinatorics/30/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Noga Alon (Princeton University and Tel Aviv University)
DTSTART:20210608T100000Z
DTEND:20210608T110000Z
DTSTAMP:20260421T084244Z
UID:RelayCombinatorics/31
DESCRIPTION:Title: <a href="https://researchseminars.org/talk/RelayCombina
 torics/31/">Splitting Random Necklaces</a>\nby Noga Alon (Princeton Univer
 sity and Tel Aviv University) as part of Round the world relay in combinat
 orics\n\n\nAbstract\nLet N be a random necklace with km beads of each of t
  types. What is the typical minimum number of points in which one can cut 
 N so that it will be possible to partition the resulting intervals of bead
 s into k collections\, each containing exactly m beads of each type ? It i
 s known that this number is at most (k-1)t with probability 1\, is it typi
 cally significantly smaller? I will discuss a recent joint work with Dor E
 lboim\, Janos Pach and Gabor Tardos addressing this problem and showing th
 at it is connected to several seemingly unrelated topics\, including match
 ings in nearly regular hypergraphs and random walks in Euclidean spaces.\n
 \nOrganized by <a href="https://combgeo.org/en/events/big-seminar/">MIPT B
 ig Seminar of Combinatorics and Geometry</a>.\n
LOCATION:https://researchseminars.org/talk/RelayCombinatorics/31/
END:VEVENT
BEGIN:VEVENT
SUMMARY:László Lovász (Eotvos University)
DTSTART:20210608T110000Z
DTEND:20210608T120000Z
DTSTAMP:20260421T084244Z
UID:RelayCombinatorics/32
DESCRIPTION:Title: <a href="https://researchseminars.org/talk/RelayCombina
 torics/32/">Orthogonal representations and graph limits</a>\nby László L
 ovász (Eotvos University) as part of Round the world relay in combinatori
 cs\n\n\nAbstract\nOrthogonal representations have played a role in informa
 tion theory\, combinatorial optimization\, rigidity theory and quantum phy
 sics. We start with a survey of these connections.\nRecent interest in thi
 s construction is motivated by graph limit theory. Limit objects of conver
 gent graph sequences have been defined in the two extreme cases: graphons 
 (limits of dense graph sequences) and graphings (limits of bounded-degree 
 graph sequences). In the middle ranges\, Markov chains seem to play an imp
 ortant role. An interesting example from this point of view is the Markov 
 chain on the sphere in a fixed dimension\, where a step is a move by 90 de
 grees in any direction.\nA basic question: is this object a limit of finit
 e graphs (and in what sense)? To get an affirmative answer\, we need to de
 fine the density of a given simple graph in the orthogonality graph. This 
 leads to the problem of defining and computing a random orthogonal represe
 ntation of this graph\, which is an interesting and nontrivial issue on it
 s own.\n\nOrganized by <a href="https://coge.elte.hu/seminar.html">Budapes
 t (BBC+G) seminar</a>.\n
LOCATION:https://researchseminars.org/talk/RelayCombinatorics/32/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Carla Groenland (Utrecht University)
DTSTART:20210608T120000Z
DTEND:20210608T130000Z
DTSTAMP:20260421T084244Z
UID:RelayCombinatorics/33
DESCRIPTION:Title: <a href="https://researchseminars.org/talk/RelayCombina
 torics/33/">Universal Graphs and Labelling Schemes</a>\nby Carla Groenland
  (Utrecht University) as part of Round the world relay in combinatorics\n\
 n\nAbstract\nAn induced universal graph for a graph class contains all gra
 phs in the class as an induced subgraph. We construct induced universal gr
 aphs for all hereditary graph classes\, and derive reachability labelling 
 schemes for digraphs and comparability labelling schemes for posets from t
 his. All these results are asymptotically optimal. This talk aims to give 
 some intuition about these concepts and our techniques (including Szemered
 i regularity lemma and efficient dictionaries). We will also discuss a new
  venue of research: what if we strengthen induced to isometric? Several in
 teresting questions are left open.\nThis is based on joint work with Marth
 e Bonamy\, Louis Esperet\, Cyril Gavoille and Alex Scott.\n\nOrganized by 
 <a href="https://graphesetoptimisation.labri.fr/pmwiki.php/Groupe/GT">Bord
 eaux Seminar</a>.\n
LOCATION:https://researchseminars.org/talk/RelayCombinatorics/33/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Deepak Bal (Montclair State University)
DTSTART:20210608T130000Z
DTEND:20210608T140000Z
DTSTAMP:20260421T084244Z
UID:RelayCombinatorics/34
DESCRIPTION:Title: <a href="https://researchseminars.org/talk/RelayCombina
 torics/34/">Size Ramsey numbers of paths and cycles</a>\nby Deepak Bal (Mo
 ntclair State University) as part of Round the world relay in combinatoric
 s\n\n\nAbstract\nLet $\\mathcal{F}_1$ and $\\mathcal{F}_2$ be two families
  of graphs. The size Ramsey number $\\hat R(\\mathcal{F}_1\, \\mathcal{F}_
 2)$ is the smallest number $m$ such that there exists a graph $G$ with $m$
  edges in which every red-blue coloring of $E(G)$ contains either a red gr
 aph from $\\mathcal{F}_1$ or a blue graph from $\\mathcal{F}_2$. Let $P_n$
  represent the path on $n$ vertices and let 𝒞 represent the family of a
 ll cycles. We discuss some recent progress on size Ramsey numbers in the c
 ases where $\\mathcal{F}_1=\\mathcal{F}_1=\\{P_n\\}$ (improvement of lower
  bound) and where $\\mathcal{F}_1=\\{P_n\\}$\, $\\mathcal{F}_2=\\mathcal{C
 }$ (improvement of lower and upper bounds). We will also discuss some rece
 nt results concerning the size Ramsey number of hypergraph paths. This is 
 based on joint works with DeBiasio and Schudrich.\n\nOrganized by the <a h
 ref="http://userhome.brooklyn.cuny.edu/skingan/CombinatoricsSeminar/">NYC 
 Combinatorics Seminar</a>.\n
LOCATION:https://researchseminars.org/talk/RelayCombinatorics/34/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Dhruv Mubayi (University of Illinois at Chicago)
DTSTART:20210608T140000Z
DTEND:20210608T150000Z
DTSTAMP:20260421T084244Z
UID:RelayCombinatorics/35
DESCRIPTION:Title: <a href="https://researchseminars.org/talk/RelayCombina
 torics/35/">The feasible region of hypergraphs</a>\nby Dhruv Mubayi (Unive
 rsity of Illinois at Chicago) as part of Round the world relay in combinat
 orics\n\n\nAbstract\nMany extremal hypergraph problems seek to maximize th
 e number of edges subject to some local constraints. We aim to gain a more
  detailed understanding of such problems by studying the maximum subject t
 o an additional global constraint\, namely the size of the shadow. Put dif
 ferently\, we seek the pairs (x\,y) in the unit square such that there are
  F-free hypergraphs whose shadow density approaches x and edge density app
 roaches y. I will give some general results about the shape of this "feasi
 ble region" and also extend and improve some classical Turan-type results 
 for particular choices of F. This is joint work with Xizhi Liu.\n\nOrganiz
 ed by the <a href="https://sites.google.com/view/epcwebinar/">EPC Webinar<
 /a>.\n
LOCATION:https://researchseminars.org/talk/RelayCombinatorics/35/
END:VEVENT
BEGIN:VEVENT
SUMMARY:James Davies (University of Waterloo)
DTSTART:20210608T150000Z
DTEND:20210608T160000Z
DTSTAMP:20260421T084244Z
UID:RelayCombinatorics/36
DESCRIPTION:Title: <a href="https://researchseminars.org/talk/RelayCombina
 torics/36/">Colouring circle graphs and their generalisations</a>\nby Jame
 s Davies (University of Waterloo) as part of Round the world relay in comb
 inatorics\n\n\nAbstract\nA circle graph is an intersection graph of a set 
 of chords on a circle\; vertices are adjacent whenever their corresponding
  chords intersect. A classical graph colouring result due to Gyárfás sta
 tes that circle graphs are χ-bounded\, i.e.\, circle graphs with bounded 
 clique number have bounded chromatic number. I will discuss some recent re
 sults concerning χ-boundedness of circle graphs and various more general 
 classes that contain them.\nThis talk includes joint work with Tomasz Kraw
 czyk\, Rose McCarty\, and Bartosz Walczak.\n\nOrganized by the <a href="ht
 tps://www.fi.muni.cz/dfseminar/index.html.en">Joint DIMEA and FORMELA semi
 nar</a> at Masaryk University.\n
LOCATION:https://researchseminars.org/talk/RelayCombinatorics/36/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Jacob Fox (Stanford University)
DTSTART:20210608T160000Z
DTEND:20210608T170000Z
DTSTAMP:20260421T084244Z
UID:RelayCombinatorics/37
DESCRIPTION:Title: <a href="https://researchseminars.org/talk/RelayCombina
 torics/37/">Removal lemmas</a>\nby Jacob Fox (Stanford University) as part
  of Round the world relay in combinatorics\n\n\nAbstract\nThe triangle rem
 oval lemma is a central result in extremal combinatorics\, with many appli
 cations in number theory\, graph theory\, discrete geometry\, and theoreti
 cal computer science. It says that any graph with n vertices and $o(n^3)$ 
 triangles can be made triangle-free by removing $o(n^2)$ edges. In this ta
 lk\, I will survey recent extensions and variants\, quantitative aspects\,
  applications\, and open problems.\n\nOrganized by <a href="http://people.
 maths.ox.ac.uk/scott/dmp.htm">Oxford Discrete Mathematics and Probability 
 Seminar</a>.\n
LOCATION:https://researchseminars.org/talk/RelayCombinatorics/37/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Allan Sly (Princeton University)
DTSTART:20210608T170000Z
DTEND:20210608T180000Z
DTSTAMP:20260421T084244Z
UID:RelayCombinatorics/38
DESCRIPTION:Title: <a href="https://researchseminars.org/talk/RelayCombina
 torics/38/">Spread of infections in random walkers</a>\nby Allan Sly (Prin
 ceton University) as part of Round the world relay in combinatorics\n\n\nA
 bstract\nWe consider a class of interacting particle systems where particl
 es perform independent random walks on $\\mathbb{Z}^d$ and spread an infec
 tion according to a Susceptible-Infectious-Recovered or SIR model. We show
  that if the recovery rate is low enough\, the infection spreads linearly.
  I will describe new methods to understand growth processes in such models
 .\nJoint work with Duncan Dauvergne\,\n\nOrganized by The Ohio State Unive
 rsity <a href="https://u.osu.edu/probability/">Combinatorics & Probability
  Seminar</a>.\n
LOCATION:https://researchseminars.org/talk/RelayCombinatorics/38/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Marcelo Campos (IMPA)
DTSTART:20210608T180000Z
DTEND:20210608T190000Z
DTSTAMP:20260421T084244Z
UID:RelayCombinatorics/39
DESCRIPTION:Title: <a href="https://researchseminars.org/talk/RelayCombina
 torics/39/">The singularity probability of a random symmetric matrix is ex
 ponentially small</a>\nby Marcelo Campos (IMPA) as part of Round the world
  relay in combinatorics\n\n\nAbstract\nLet $A$ be drawn uniformly at rando
 m from the set of all $n \\times n$ symmetric matrices with entries in {-1
 \,1}. I'll describe some recent work where we show that $P(det(A) = 0) < e
 ^{-cn}$ for some absolute constant $c > 0$.\nJoint work with Matthew Jenss
 en\, Marcus Michelen and Julian Sahasrabudhe.\n\nOrganized by the Rio Semi
 nar.\n
LOCATION:https://researchseminars.org/talk/RelayCombinatorics/39/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Jim Geelen (University of Waterloo)
DTSTART:20210608T190000Z
DTEND:20210608T200000Z
DTSTAMP:20260421T084244Z
UID:RelayCombinatorics/40
DESCRIPTION:Title: <a href="https://researchseminars.org/talk/RelayCombina
 torics/40/">Homomorphisms and colouring for graphs and binary matroids</a>
 \nby Jim Geelen (University of Waterloo) as part of Round the world relay 
 in combinatorics\n\n\nAbstract\nThe talk starts with Rödl's Theorem that 
 graphs with huge chromatic number contain triangle-free subgraphs with lar
 ge chromatic number. We will look at various related results and conjectur
 es\, with a notable matroid bias\; the new results are joint work with Pet
 er Nelson and Raphael Steiner.\n\nOrganized by the <a href="https://people
 .math.gatech.edu/~abernshteyn3/gt_gt/">Georgia Tech Graph Theory Seminar</
 a>.\n
LOCATION:https://researchseminars.org/talk/RelayCombinatorics/40/
END:VEVENT
BEGIN:VEVENT
SUMMARY:David Conlon (Caltech)
DTSTART:20210608T200000Z
DTEND:20210608T210000Z
DTSTAMP:20260421T084244Z
UID:RelayCombinatorics/41
DESCRIPTION:Title: <a href="https://researchseminars.org/talk/RelayCombina
 torics/41/">Random multilinear maps and the Erdős box problem</a>\nby Dav
 id Conlon (Caltech) as part of Round the world relay in combinatorics\n\n\
 nAbstract\nBy using random multilinear maps\, we provide new lower bounds 
 for the Erdős box problem\, the problem of estimating the extremal number
  of the complete d-partite d-uniform hypergraph with two vertices in each 
 part\, thereby improving on work of Gunderson\, Rödl and Sidorenko. Joint
  work with Cosmin Pohoata and Dmitriy Zakharov.\n\nOrganized by <a href="h
 ttps://sites.google.com/view/agco-seminar-chile/home">AGCO Seminar</a>.\n
LOCATION:https://researchseminars.org/talk/RelayCombinatorics/41/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Fan Chung (UCSD)
DTSTART:20210608T210000Z
DTEND:20210608T220000Z
DTSTAMP:20260421T084244Z
UID:RelayCombinatorics/42
DESCRIPTION:Title: <a href="https://researchseminars.org/talk/RelayCombina
 torics/42/">Trees and forests in Green's functions of a graph</a>\nby Fan 
 Chung (UCSD) as part of Round the world relay in combinatorics\n\n\nAbstra
 ct\nThe Green's functions of a graph are the pseudo inverses of the Laplac
 ians and therefore are useful for solving many types of Laplace equations 
 in discrete settings.\nIn this talk\, we will give combinatorial interpret
 ations of Green's functions in terms of Counting trees and forests in a gr
 aph. We will also mention several applications concerning the pagerank alg
 orithms and the hitting time for random walks.\n\nOrganized by <a href="ht
 tps://www.sfu.ca/math/research/discrete-mathematics/discrete-math-seminars
 .html">Discrete Math Seminar</a> at Simon Fraser University.\n
LOCATION:https://researchseminars.org/talk/RelayCombinatorics/42/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Andrew Suk (UCSD)
DTSTART:20210608T220000Z
DTEND:20210608T230000Z
DTSTAMP:20260421T084244Z
UID:RelayCombinatorics/43
DESCRIPTION:Title: <a href="https://researchseminars.org/talk/RelayCombina
 torics/43/">Turán-type problems for point-line incidences</a>\nby Andrew 
 Suk (UCSD) as part of Round the world relay in combinatorics\n\n\nAbstract
 \nIn this talk\, I will discuss several Turán-type results for point-line
  incidences. It will be based on joint works with Istvan Tomon and Mozhgan
  Mirzaei.\n\nOrganized by <a href="https://www.uvic.ca/science/math-statis
 tics/home/home/events/seminars/discrete-math/index.php">University of Vict
 oria Discrete Math Seminar</a>.\n
LOCATION:https://researchseminars.org/talk/RelayCombinatorics/43/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Ron Gould (Emory)
DTSTART:20210608T230000Z
DTEND:20210608T235900Z
DTSTAMP:20260421T084244Z
UID:RelayCombinatorics/44
DESCRIPTION:Title: <a href="https://researchseminars.org/talk/RelayCombina
 torics/44/">Chorded cycles</a>\nby Ron Gould (Emory) as part of Round the 
 world relay in combinatorics\n\n\nAbstract\nA chord of a cycle is an edge 
 between two vertices of the cycle that is not an edge of the cycle. A cycl
 e in a graph G is said to be chorded if its vertices induce at least one c
 hord\, and it is called doubly chorded if its vertices induce two or more 
 chords. The past decade has seen a vast increase in the study of chorded c
 ycles.\nIn this talk I will survey a variety of results dealing with chord
 ed cycles. I will consider several types of questions dealing with chorded
  cycles and con- sider the major known results in each of these areas. Thi
 s includes minimum degree and degree sum results\, forbidden subgraph resu
 lts\, and edge density results. We will ask questions like:` When can an e
 dge be a chord of a cycle and when can an edge be a cycle edge of a chorde
 d cycle? Many times\, I will try to place these chorded cycle results in r
 elation to known results on cycles and show that the chorded cycle results
  are actually natural extensions of known cycle results.\n\nOrganized by t
 he Discrete Maths Seminar at University of Alaska\, Fairbanks.\n
LOCATION:https://researchseminars.org/talk/RelayCombinatorics/44/
END:VEVENT
END:VCALENDAR