Cubic gradient nonlinearity
= Cubic gradient nonlinearity
{title2=$N(u)=|Du|^2u$}
In three dimensions the map $N(u)=|Du|^2u$ sends $H^2$ into $L^2$, because $H^2\hookrightarrow W^{1,4}\cap L^\infty$. On an $H^2$ ball of radius $R$ it is locally Lipschitz with constant $O(R^2)$.