\left[ \begin{array}{cc} a & b \\
c & d \end{array} \right] \in M2(R) \vert A( \left[ \begin{array}{cc} a & b \\
c & d \end{array} \right] ) = \left[ \begin{array}{cc} 0 & 0 \\
0 & 0 \end{array} \right]