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