Solution (source code)

= Solution

Let $V$ be the enclosed region with piecewise smooth closed boundary $S$, oriented by its outward <unit normal> $\mathbf n$. For a continuously <differentiable> <vector field> on a neighbourhood of $V$, the <divergence theorem> states
$$
\boxed{\oiint_S\mathbf F\cdot\mathbf n\,dS
=\iiint_V\nabla\cdot\mathbf F\,dV}.
$$
The outward <flux integral> equals the <volume integral> of the <divergence>.