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arXiv · 2409.09397

Trees and near-linear stable sets

Tung Nguyen·Alex Scott·Paul Seymour
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Abstract

When $H$ is a forest, the Gy\'arf\'as-Sumner conjecture implies that every graph $G$ with no induced subgraph isomorphic to $H$ and with bounded clique number has a stable set of linear size. We cannot prove that, but we prove that every such graph $G$ has a stable set of size $|G|^{1-o(1)}$. If $H$ is not a forest, there need not be such a stable set. Second, we prove that when $H$ is a ``multibroom'', there {\em is} a stable set of linear size. As a consequence, we deduce that all multibrooms satisfy a ``fractional colouring'' version of the Gy\'arf\'as-Sumner conjecture. Finally, we discuss extensions of our results to the multicolour setting.

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Tung Nguyen, Alex Scott, Paul Seymour. 2024-09-14. Trees and near-linear stable sets. https://arxiv.org/abs/2409.09397

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