Separating a chart
  In this paper, we shall show a condition for that a chart is C-move equivalent to the product of two charts, the union of two charts $\Gamma^*$ and $\Gamma^{**}$ which are contained in disks $D^*$ and $D^{**}$ with $D^*\cap D^{**}=\emptyset$. 
Teruo Nagase and Akiko Shima
math.GT