$\displaystyle\frac{{{m}{{n}}^{{3}}}}{{{{m}}^{{2}}{{n}}^{{4}}}}\usepackage{cmbright}\Huge\$ , domain all m, $\displaystyle{m}\ne{0}\usepackage{cmbright}\Huge\$ and all n, $\displaystyle{n}\ne{0}\usepackage{cmbright}\Huge\$