Properties of minimal charts and their applications VIII: charts of type $(7)$

Abstract

Let $\Gamma$ be a chart, and we denote by $\Gamma_m$ the union of all the edges of label $m$. A chart $\Gamma$ is of type $(7)$ if there exists a label $m$ such that $w(\Gamma)=7$, $w(\Gamma_m\cap\Gamma_{m+1})=7$ where $w(G)$ is the number of white vertices in $G$. In this paper, we prove that there is no minimal chart of type $(7)$.