Solution (source code)

= Solution

For a twice continuously <differentiable> scalar potential, the <curl> of its <gradient> is
$$
\nabla\times\nabla\Phi
=(\Phi_{zy}-\Phi_{yz},\ \Phi_{xz}-\Phi_{zx},\ \Phi_{yx}-\Phi_{xy}).
$$
Equality of mixed <partial derivatives> makes every component zero. Thus
$$
\boxed{\nabla\times\mathbf F=0}.
$$
This is the <curl of a gradient> identity.