A=E_{1}E_{2}...E_{k}D_{1}F_{1}F_{2}...F_{l}=E_{1}E_{2}...E_{k}\left ( \begin{array}{ccc} 1 \\ 0 \\ 0 \\ \vdots \\ 0 \end{array} \right) \left ( \begin{array}{ccc} 1 & 0 & \dots \ 0 \end{array} \right )F_{1}F_{2}...F_{l}.