%indent
$$$
\:Test \:Test \mathbb{N} e^{i\theta} \int\!\!\!\!\int\! F dx dy
$$$
$$$
\ffd{a}{b} \ffd{a}{\ffd{b}{c}} \ffd{\ffd{b}{c}}{a} \ffd{\ffd{a}{b}}{\ffd{c}{d}}
$$$
$$$
\ddd{a}{b} \ddd{a}{\ddd{b}{c}} \ddd{\ddd{b}{c}}{a} \ddd{\ddd{a}{b}}{\ddd{c}{d}}
$$$
$$$
$\ppd{a}{b} \ppd{a}{\ppd{b}{c}} \ppd{\ppd{b}{c}}{a} \ppd{\ppd{a}{b}}{\ppd{c}{d}}
$$$