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Casey Tompkins, 3-uniform hypergraphs avoiding a cycle of length four
Casey Tompkins, 3-uniform hypergraphs avoiding a cycle of length four
We show that that the maximum number of of edges in a
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Discrete Math Seminar
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Rutger Campbell, Matroid orientability and representability
Rutger Campbell, Matroid orientability and representability
In this talk we will have a brief introduction to oriented matroids and their relation to real-representability.
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William Overman, Some Ordered Ramsey Numbers of Graphs on Four Vertices
William Overman, Some Ordered Ramsey Numbers of Graphs on Four Vertices
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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Sang-il Oum (엄상일), What is an isotropic system?
Sang-il Oum (엄상일), What is an isotropic system?
Bouchet introduced isotropic systems in 1983 unifying some combinatorial features of binary matroids and 4-regular graphs. The concept of isotropic system is a useful tool to study vertex-minors of graphs and yet it is not well known. I will give an introduction to isotropic systems.
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Jungho Ahn (안정호), Well-partitioned chordal graphs with the obstruction set and applications
Jungho Ahn (안정호), Well-partitioned chordal graphs with the obstruction set and applications
We introduce a new subclass of chordal graphs that generalizes split graphs, which we call well-partitioned chordal graphs. Split graphs are graphs that admit a partition of the vertex set into cliques that can be arranged in a star structure, the leaves of which are of size one. Well-partitioned chordal graphs are a generalization of …