TeX source:
\begin{array}{crclcl} & \mathbb{D} &=& \mathbb{R} \cr\cr & 0 &=& x e^x &\vert& \text{Satz vom Nullprodukt} \cr \text{Faktor 1:} & 0 &=& x \cr\cr \text{Faktor 2:} & 0 &=& e^x \end{array}