| 日時 | 2021年12月13日(月)16:30-- |
|---|---|
| 場所 | オンライン |
| 講演者 | 江川 嘉美（東京理科大学） |
| 講演題目 | Forbidden caterpillars for 3-connected graphs with girth at least five |
| 日時 | 2021年11月22日(月)16:30-- |
|---|---|
| 場所 | オンライン |
| 講演者 | 八島 高将（成蹊大学） |
| 講演題目 | k-閉路のみからなる 2-因子のみをもつような 2-連結 3-正則グラフ |
| 日時 | 2021年11月1日(月)16:30-- |
|---|---|
| 場所 | オンライン |
| 講演者 | 野口 健太（東京理科大学） |
| 講演題目 | 射影平面の三角形分割の全域四角形分割 |
| 日時 | 2021年10月18日(月)16:30-- |
|---|---|
| 場所 | オンライン |
| 講演者 | 前澤 俊一（電気通信大学） |
| 講演題目 | 外平面的グラフのDP-degree-coloring |
| 日時 | 2021年10月4日(月)16:30-- |
|---|---|
| 場所 | オンライン |
| 講演者 | 江川 嘉美（東京理科大学） |
| 講演題目 | Contractible edges and longest cycles in 3-connected graphs |
| 日時 | 2021年7月5日(月)16:30-- |
|---|---|
| 場所 | オンライン |
| 講演者 | Morteza Hasanvand（Sharif University） |
| 講演題目 | Edge-decomposition of graphs into 3-paths and 4-paths |
| 講演内容 | In 2008 Thomassen showed that a large enough edge-connectivity is a sufficient condition for decomposing a graph into isomorphic copies of two small trees and concluded the following results: (i) A 171-edge-connected simple graph has an edge-decomposition into paths of length 3 if and only if its size is divisible by 3, (ii) A 10^10^10^14-edge-connected simple graph has an edge-decomposition into paths of length 4 if and only if its size is divisible by 4. These numbers were recently pushed down by several authors. In this talk, we discuss about some new sufficient conditions for the existence of such path edge-decompositions. |
| 日時 | 2021年6月21日(月)16:30-- |
|---|---|
| 場所 | オンライン |
| 講演者 | 藤沢 潤（慶應義塾大学） |
| 講演題目 | 閉曲面上のグラフにおけるマッチング拡張問題の一般化 |
| 日時 | 2021年6月14日(月)16:30-- |
|---|---|
| 場所 | オンライン |
| 講演者 | Yaping Mao（Qinghai Normal University） |
| 講演題目 | Some Topics on the Gallai-Ramsey Theory |
| 講演内容 | Ramsey type problem has been a hot topic in mathematics for decades now due to their intrinsic beauty, wide applicability, and overwhelming difficulty despite somewhat misleadingly simple statements. A coloring of a graph is called rainbow if no two edges have the same color. Colorings of complete graphs that contain no rainbow triangle have very interesting and somewhat surprising structure. In 1967, Gallai first examined this structure under the guise of transitive orientations. In this talk, we extended this idea from graph theory to the other three mathematical branches, and introduce some preliminary results on the Graph Gallai-Ramsey Theory, Euclidean Gallai-Ramsey Theory, Integer Gallai-Ramsey Theory, and Lattice Ramsey Theory. |
| 日時 | 2021年5月17日(月)17:00-- |
|---|---|
| 場所 | オンライン |
| 講演者 | Carol T. Zamfirescu (Ghent University) |
| 講演題目 | On two conjectures of Grunbaum concerning longest cycles |
| 講演内容 | Motivated by two conjectures of Grunbaum on graphs and their longest cycles -- one settled by Thomassen, one widely open -- we discuss in this talk the relationship between the hamiltonicity of a graph and (i) the hamiltonicity of its vertex-deleted subgraphs in the first part, and (ii) the hamiltonicity of its K_2-deleted subgraphs in the second part. A special focus will lie on the planar case. For part (i), we present results on non-hamiltonian graphs in which every vertex-deleted subgraph is hamiltonian as well as extensions of theorems of Tutte and Thomassen on the hamiltonicity of planar graphs and their vertex-deleted subgraphs. Regarding part (ii), we shall recall a conjecture of Grunbaum, relate it to a problem of Katona, Kostochka, Pach, and Stechkin, and present recent results on a special case thereof. |