Author

Ekkehard Köhler

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Preprint Oct 2026

W[1]-Hardness of Upper Clique Transversal

A clique transversal of a graph is a set of vertices intersecting every maximal clique. We prove that deciding whether a graph has an inclusion-wise minimal clique transversal of size at least $k$ is W[1]-hard when parameterized by $k$.

Pascal Gollin, Tesshu Hanaka, Ekkehard Köhler et al. · 0 citations

Preprint Sep 2026

On Kernels and Leaves: Searching for Bare and Lush Trees

We study a variation of the classical Maximum (Minimum) Leaf Spanning Tree problem. In many applications, Depth-First Search (DFS) is used to compute a spanning tree of a graph. Such a search tree is constructed by connecting each vertex $v$ with the last vertex the search has visited before $v$ and we call this a last...

Jesse Beisegel, Ekkehard Köhler, R. Scheffler et al. · 0 citations