English

4K_1 free graphs on 13 vertices have cop number at most 2

Combinatorics 2026-01-15 v2

Abstract

The game of cops and robber has been studied for many years. Denoting Forb(4K1)\mathsf{Forb}(4K_1) to be the family of all graphs that contain no induced subgraph isomorphic to 4K14K_1 (e.g., with independence number less than 44), we prove that for any GForb(4K1)G\in\mathsf{Forb}(4K_1), we have c(G)2c(G)\leq 2, where c()c(\cdot) is the cop number. This improves a lower bound of a question proposed by Char et al. in a recent paper (arxiv, 2025), that any counterexample of a conjecture raised by Turcotte (2022) when p=4p=4 must have at least 14 vertices.

Keywords

Cite

@article{arxiv.2601.00917,
  title  = {4K_1 free graphs on 13 vertices have cop number at most 2},
  author = {Zhaoyu Wu},
  journal= {arXiv preprint arXiv:2601.00917},
  year   = {2026}
}