\begin{bmatrix}
0 & 0 & 0 &  0 & 0 &  0 & 0 &  0 \\
1 & 1 & 0 & -1 & 0 &  0 & 0 &  0 \\
0 & 0 & 1 &  0 & 1 & -1 & 0 &  0 \\
0 & 0 & 0 &  0 & 0 &  0 & 1 & -1
\end{bmatrix}