TeX source:
\begin{array}{rclcl} 0 &=& x^2-4 &\vert& +4 \cr x^2 &=& 4 &\vert& \pm\sqrt{} \cr\cr x_1 &=& -2 \cr x_2 &=& 2 \cr\cr \mathbb{L} &=& \{-13;-2;2\} \end{array}