For a one-degree-of-freedom system, prove that the phase-space transformation Q = {\left(q − p\right)}/{\sqrt{2}} , P = {\left(q + p\right)}/{\sqrt{2}} is canonical.
The straightforward computation
M^{T}JM =\frac{1}{2}\begin{pmatrix} 1 & 1 \\ -1 & 1 \end{pmatrix} \begin{pmatrix} 0 & 1 \\ -1 & 0 \end{pmatrix} \begin{pmatrix} 1 & -1 \\ 1 & 1 \end{pmatrix}
= \frac{1}{2}\begin{pmatrix} 0 & 2 \\ -2 & 0 \end{pmatrix}=\begin{pmatrix} 0 & 1 \\ -1 & 0 \end{pmatrix}=J
establishes the canonical nature of the transformation.