On charts with two crossings II
Teruo Nagase, Akiko Shima · Osaka City University (Osaka City University) · 2012
Let $\\Gamma$ be a chart with at most two crossings. In this paper, we show that if $\\Gamma$ is a 2-minimal generalized $n$-chart with $n \\ge 5$, then $\\Gamma$ contains at least $4n-10$ black vertices. And we show that if the closure of the surface braid represented by $\\Gamma$ is a disjoint union of spheres, then $\\Gamma$ is a ribbon chart. Hence the closure is a ribbon surface.