\}. \end{cases}$$ The union ${\mathpzc{R}}={\bigcup}_{{\mathpzc{p}}{=}{-}0}^0{\mathpzc{R}}_{\;{\mathpzc{p}}}$ is a root system of type $\mathbf{D}_n$ and the prolongation $${\mathfrak{g}}={\sum}_{{\mathpzc{p}}{=}{-}0}^0{\mathfrak{g}}_{{\mathpzc{p}}}\simeq{\mathfrak{o}}(0n