Hardy inequality in Euclidean space (source code)

= Hardy inequality in Euclidean space
{c}
{wiki=Hardy's_inequality}

For $d\geq3$ and $u\in H^1(\mathbb R^d)$,
$$
\int_{\mathbb R^d}\frac{|u(x)|^2}{|x|^2}\,dx
\leq\frac{4}{(d-2)^2}\int_{\mathbb R^d}|\nabla u(x)|^2\,dx.
$$