Ron Aharoni, A strong version of the Caccetta-Haggkvist conjecture
The Caccetta-Haggkvist conjecture, one of the best known in graph theory, is that in a digraph with $n$ vertices in which all outdegrees are at least $n/k$ there is a …
10 events found.
Virtual Discrete Math Colloquium
Events
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Zoom ID: 869 4632 6610 (ibsdimag)
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Ken-ichi Kawarabayashi (河原林 健一), Toward Directed Graph Minor Theory
Zoom ID: 869 4632 6610 (ibsdimag)Graph Minor project by Robertson and Seymour is perhaps the deepest theory in Graph Theory. It gives a deep structural characterization of graphs without any graph $H$ as a minor. …
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Bo Ning (宁博), Substructures and eigenvalues of graphs: Triangles and quadrilaterals
Zoom ID: 869 4632 6610 (ibsdimag)Our talk will mainly focus on the relationship between substructures and eigenvalues of graphs. We will briefly survey recent developments on a conjecture of Bollobás and Nikiforov and a classical …
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James Davies, Separating polynomial $\chi$-boundedness from $\chi$-boundedness
Zoom ID: 869 4632 6610 (ibsdimag)We prove that there is a function $f : \mathbb{N} \to \mathbb{N}$ such that for every function $g : \mathbb{N} \to \mathbb{N} \cup \{\infty\}$ with $g(1)=1$ and $g \ge f$, …
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Manuel Lafond, Recognizing k-leaf powers in polynomial time, for constant k
Zoom ID: 869 4632 6610 (ibsdimag)A graph G is a k-leaf power if there exists a tree T whose leaf set is V(G), and such that uv is an edge if and only if the …
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Fedor Fomin, Long cycles in graphs: Extremal Combinatorics meets Parameterized Algorithms
Zoom ID: 869 4632 6610 (ibsdimag)We examine algorithmic extensions of two classic results of extremal combinatorics. First, the theorem of Dirac from 1952 asserts that a 2-connected graph G with the minimum vertex degree d>1, …
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Jean-Florent Raymond, Long induced paths in minor-closed graph classes and beyond
Zoom ID: 869 4632 6610 (ibsdimag)In 1982 Galvin, Rival, and Sands proved that in $K_{t,t}$-subgraph free graphs (t being fixed), the existence of a path of order n guarantees the existence of an induced path …
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Jakub Gajarský, Model Checking on Interpretations of Classes of Bounded Local Clique-Width
Zoom ID: 869 4632 6610 (ibsdimag)The first-order model checking problem for finite graphs asks, given a graph G and a first-order sentence $\phi$ as input, to decide whether $\phi$ holds on G. Showing the existence …
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Michael Savery, Induced subgraphs of induced subgraphs of large chromatic number
Zoom ID: 869 4632 6610 (ibsdimag)We prove that for every graph F with at least one edge there are graphs H of arbitrarily large chromatic number and the same clique number as F such that …
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Jan Kurkofka, Canonical Graph Decompositions via Coverings
Zoom ID: 869 4632 6610 (ibsdimag)We present a canonical way to decompose finite graphs into highly connected local parts. The decomposition depends only on an integer parameter whose choice sets the intended degree of locality. …