$χ$-binding function for a superclass of $2K_2$-free graphs (2207.08168v1)

Abstract: The class of $2K_2$-free graphs has been well studied in various contexts in the past. In this paper, we study the chromatic number of ${butterfly, hammer}$-free graphs, a superclass of $2K_2$-free graphs and show that a connected ${butterfly, hammer}$-free graph $G$ with $\omega(G)\neq 2$ admits $\binom{\omega+1}{2}$ as a $\chi$-binding function which is also the best available $\chi$-binding function for its subclass of $2K_2$-free graphs. In addition, we show that if $H\in{C_4+K_p, P_4+K_p}$, then any ${butterfly, hammer, H}$-free graph $G$ with no components of clique size two admits a linear $\chi$-binding function. Furthermore, we also establish that any connected ${butterfly, hammer, H}$-free graph $G$ where $H\in {(K_1\cup K_2)+K_p, 2K_1+K_p}$, is perfect for $\omega(G)\geq 2p$.