We prove that every connected $P_5$-free graph has cop number at most two, solving a conjecture of Sivaraman. In order to do so, we first prove that every connected $P_5$-free graph $G$ with independence number at least three contains a three-vertex induced path with vertices $a \hbox{-} b \hbox{-} c$ in order, such that every neighbour of $c$ is also adjacent to one of $a,b$.
翻译:我们证明每个连接到的无P$5美元的图表最多有2个警察号码,解决了Sivaraman的猜测。为了做到这一点,我们首先证明,每个连接到P$5美元的无G美元图上与独立数字至少有3个包含一个3个顶端诱导路径,上面有1美元\hbox{-}b\hbox{-}c$,这样每个相邻的C$也都与1美元/b美元相邻。