\newcommand{\bm}[1]{\boldsymbol{#1}}
\displaystyle\div\bm{D}\cdot d\bm{s} &=& Q\\
\displaystyle -\dot{\bm B}\cdot &=& \operatorname{rot }\bm E\\\displaystyle \oint_S \bmoperatorname{Hrot}\cdot d\bm{sH} &=& I \bm i\\
(\iff 4\pi r^2d\bm{H} &=&
d\bm{i}\times\hat{\bm{r}})
