Show that the map $\omega _ { 0 }$ defined by
$$\begin{array} { r l c c } \omega _ { 0 } : & \mathbb { R } ^ { n } \times \mathbb { R } ^ { n } & \rightarrow & \mathbb { R } \\ ( X , Y ) & \mapsto & { } ^ { t } X J _ { n } Y \end{array}$$
is a symplectic form on $\mathbb { R } ^ { n }$.