Classification of isolated singularities for nonhomogeneous operators in divergence form (Q491503)

The author is concerned with the equation \(\text{div}(\frac{\varphi(|\nabla u|)}{|\nabla u|}\nabla u)=0\) in the punctured ball of \(\mathbb{R}^N\), \(N\geq 2\). Here \(\varphi\) is an odd increasing \(C^1\) homeomorphism of the real line into itself. The main result of the paper establishes that any non-negative solution has either a removable singularity at the origin or behaves like the fundamental solution around the origin.