English

Cops and Robbers, Clique Covers, and Induced Cycles

Combinatorics 2025-07-22 v1 Discrete Mathematics

Abstract

We consider the Cops and Robbers game played on finite simple graphs. In a graph GG, the number of cops required to capture a robber in the Cops and Robbers game is denoted by c(G)c(G). For all graphs GG, c(G)α(G)θ(G)c(G) \leq \alpha(G) \leq \theta(G) where α(G)\alpha(G) and θ(G)\theta(G) are the independence number and clique cover number respectively. In 2022 Turcotte asked if c(G)<α(G)c(G) < \alpha(G) for all graphs with α(G)3\alpha(G) \geq 3. Recently, Char, Maniya, and Pradhan proved this is false, at least when α=3\alpha = 3,by demonstrating the compliment of the Shrikhande graph has cop number and independence number 33. We prove, using random graphs, the stronger result that for all k1k\geq 1 there exists a graph GG such that c(G)=α(G)=θ(G)=kc(G) = \alpha(G) = \theta(G) = k. Next, we consider the structure of graphs with c(G)=θ(G)3c(G) = \theta(G) \geq 3. We prove, using structural arguments, that any graphs GG which satisfies c(G)=θ(G)=k3c(G) = \theta(G) = k \geq 3 contain induced cycles of all lengths 3tk+13\leq t \leq k+1. This implies all perfect graphs GG with α(G)4\alpha(G)\geq 4 have c(G)<α(G)c(G) < \alpha(G). Additionally,we discuss if typical triangle-free and C4C_4-free graphs will have c(G)<α(G)c(G) < \alpha(G).

Keywords

Cite

@article{arxiv.2507.14321,
  title  = {Cops and Robbers, Clique Covers, and Induced Cycles},
  author = {Alexander Clow and Imed Zaguia},
  journal= {arXiv preprint arXiv:2507.14321},
  year   = {2025}
}

Comments

15 pages, 1 figure