\end{array}\right)\to\left(\begin{array}{ccc}
2 & 0 & 1\\
0 & 0 & -1\\
0 & 1 & 2
\end{array}\right)\to\left(\begin{array}{ccc}
0 & 0 & -1
\end{array}\right)\to\left(\begin{array}{ccc}
2 & 0 & 1 & 1\\0 & 1 & 2 & 1\\0 & 0 & 1 & 2
\end{array}\right)\to\left(\begin{array}{ccc}
2 & 0 & 0 \\