\[\left( m^{2} - n \right)\left( m - n^{2} \right) =\]
\[= m^{2} \cdot m + m^{2} \cdot \left( - n^{2} \right) - n \cdot m - n \cdot \left( - n^{2} \right) =\]
\[= m^{2 + 1} - m^{2}n^{2} - mn + n^{1 + 2} =\]
\[= m^{3} - m^{2}n^{2} - mn + n^{3}\text{.\ }\]