Example SS Some submatrices

For the matrix \begin{equation*} A= \begin{bmatrix} 1 & -2 & 3 & 9\\ 4 & -2 & 0 & 1\\ 3 & 5 & 2 & 1 \end{bmatrix} \end{equation*} we have the submatrices \begin{align*} \submatrix{A}{2}{3} = \begin{bmatrix} 1 & -2 & 9\\ 3 & 5 & 1 \end{bmatrix} && \submatrix{A}{3}{1} = \begin{bmatrix} -2 & 3 & 9\\ -2 & 0 & 1 \end{bmatrix} \end{align*}