Debsoumya Chakraborti, Some classical problems in graph saturation

Room B232 IBS (기초과학연구원)

Graph saturation is one of the oldest areas of investigation in extremal combinatorics. A graph $G$ is called $F$-saturated if $G$ does not contain a subgraph isomorphic to $F$, but the addition of any edge creates a copy of $F$. The function $\operatorname{sat}(n,F)$ is defined to be the minimum number of edges in an $n$-vertex

Se-Young Yun (윤세영), Regret in Online Recommendation Systems

Room B232 IBS (기초과학연구원)

We propose a theoretical analysis of recommendation systems in an online setting, where items are sequentially recommended to users over time. In each round, a user, randomly picked from a population of m users, requests a recommendation. The decision-maker observes the user and selects an item from a catalogue of n items. Importantly, an item

Yixin Cao (操宜新), Recognizing (unit) interval graphs by zigzag graph searches

Room B232 IBS (기초과학연구원)

Corneil, Olariu, and Stewart presented a recognition algorithm for interval graphs by six graph searches. Li and Wu simplified it to only four. The great simplicity of the latter algorithm is however eclipsed by the complicated and long proofs. The main purpose of this paper is to present a new and significantly shorter proof for

Hong Liu (刘鸿), Nested cycles with no geometric crossing

Room B232 IBS (기초과학연구원)

In 1975, Erdős asked the following question: what is the smallest function $f(n)$ for which all graphs with $n$ vertices and $f(n)$ edges contain two edge-disjoint cycles $C_1$ and $C_2$, such that the vertex set of $C_2$ is a subset of the vertex set of $C_1$ and their cyclic orderings of the vertices respect each

Édouard Bonnet, Twin-width and ordered binary structures

Zoom ID: 869 4632 6610 (ibsdimag)

The twin-width of a graph G can be defined as the least integer d such that there is a sequence of length |V(G)| of (strictly) coarser and coarser partitions of its vertex set V(G), and every part X of every partition P of the sequence has at most d other parts Y of P with

Casey Tompkins, 3-uniform hypergraphs avoiding a cycle of length four

Room B232 IBS (기초과학연구원)

We show that that the maximum number of of edges in a $3$-uniform hypergraph without a Berge-cycle of length four is at most $(1+o(1)) \frac{n^{3/2}}{\sqrt{10}}$. This improves earlier estimates by Győri and Lemons and by Füredi and Özkahya. Joint work with Ergemlidze, Győri, Methuku, Salia.

Sophie Spirkl, Pure pairs in ordered graphs

Zoom ID: 869 4632 6610 (ibsdimag)

A pure pair in a graph G is a pair of subsets A, B of the vertex set of G such that in G, either all of the edges or none of the edges between A and B are present. Pure pairs have been studied recently motivated by their connections to the Erdos-Hajnal conjecture. In

Michał Pilipczuk, Structural properties of powers of sparse graphs

Zoom ID: 869 4632 6610 (ibsdimag)

For a graph G and an integer d, the dth power of G is the graph $G^d$ on the same vertex set as G where two vertices are considered adjacent if and only if they are at distance at most d in G. Assuming that G is sparse, what can we say about the structure

William Overman, Some Ordered Ramsey Numbers of Graphs on Four Vertices

Room B232 IBS (기초과학연구원)

Ordered Ramsey numbers were introduced in 2014 by Conlon, Fox, Lee, and Sudakov. Their results included upper bounds for general graphs and lower bounds showing separation from classical Ramsey numbers. We show the first nontrivial results for ordered Ramsey numbers of specific small graphs. In particular we prove upper bounds for orderings of graphs on four vertices,

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