Equation 3.4.1378BEC0BF5E07

\begin{equation} u*\rho _\varepsilon (x)\downarrow u(x)\quad (\varepsilon \downarrow 0),\qquad u(x)=\lim _{r\downarrow 0}\frac{1}{|B(x,r)|}\int _{B(x,r)}u(y)\, \mathrm d y. \end{equation}