$$\left[\begin{array}{cc}\hfill {\displaystyle \frac{\partial x_1}{\partial y_1}}\hfill & \hfill {\displaystyle \frac{\partial x_2}{\partial y_1}}\hfill \\ \hfill \hfill \\ \hfill {\displaystyle \frac{\partial x_1}{\partial y_2}}\hfill & \hfill {\displaystyle \frac{\partial x_2}{\partial y_2}}\hfill \end{array}\right]\left(\begin{array}{cc}\hfill 1\hfill & \hfill 2\hfill \\ \hfill 3\hfill & \hfill 4\hfill \end{array}\right)\left\{\begin{array}{cc}\hfill 1\hfill & \hfill 2\hfill \\ \hfill 3\hfill & \hfill 4\hfill \end{array}\right\}\mid \begin{array}{cc}\hfill 1\hfill & \hfill 2\hfill \\ \hfill 3\hfill & \hfill 4\hfill \end{array}\mid \parallel \begin{array}{cc}\hfill 1\hfill & \hfill 2\hfill \\ \hfill 3\hfill & \hfill 4\hfill \end{array}\parallel$$