Weakly Disk-Busting Curves in the Boundary of a Compression Body

Abstract

Let $V$ be a nontrivial compression body which is not simple. An essential simple closed curve $J$ in $\partial_+V$ is called weakly disk-busting if $\partial_+V-J$ has only one compressing disk up to isotopy. In this paper, we give an upper bound of the diameter of the image of boundaries of essential disks in $V$ under any projection determined by a weakly disk-busting curve. Moreover, we give a sufficient condition for the handle additions to be boundary irreducible.