Es sei eine Reihe

${\displaystyle \sum _{i=1}^{\infty }a_{i}10^{-i}}$

${\displaystyle {}a_{i}\in \mathbb {C} }$

${\displaystyle {}\vert {a_{i}}\vert \leq 9^{i}}$

${\displaystyle {}i\in \mathbb {N} _{+}}$