A $wheel$ is the graph consisting of a chordless cycle $C$ on at least four vertices plus an additional vertex adjacent to all the vertices of $C$. In this paper, we explore the structure of ($P_5$, wheel)-free graphs, and show that every such graph $G$ is either perfect, or a quasi-line graph, or has a clique cutset, or $G$ belongs to some well-defined special classes of graphs. This result enables us to show that every ($P_5$, wheel)-free graph $G$ satisfies $\chi(G)\leq \frac{3}{2}\omega(G)$. Moreover, this bound is asymptotically tight. That is, there is a class of ($P_5$, wheel)-free graphs $\cal L$ such that every graph $H\in \cal L$ satisfies $\chi(H)\geq\frac{10}{7}\omega(H)$.
翻译:$wal$ 是一个由至少四个顶点上一个无弦周期的C$组成的图表。 在本文中, 我们探索无轮图的结构 ($_ 5$, 轮式), 并显示每张无轮式G$ 是完美的, 或准线图, 或有一个圆形切片, 或 $G$ 属于某些定义明确的特殊图表类别 。 这个结果让我们能够显示每张无轮式( P_ 5$, 轮式) 图形 $\ chi( G)\\leq\\ leq\\ frac{ 3 ⁇ 2\ omga( G)$ 。 此外, 这个圈子太紧了。 也就是说, 每一张无轮式的G$5$, 也就是每张H\ 美元 美元 / clex $\ clex $\\ lech\\ lech (H)\ g\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\