 $$m\left (\begin{array}{cc} 0 & c\\ 0 & y \end{array} \right) = (m\varepsilon_Y)\left (\begin{array}{cc} 0 & c\\ 0 & y \end{array} \right) =m\left (\begin{array}{cc} 0 & 0\\ 0 & y \end{array} \right).$$ 