Preliminaries

Let \(G\subset \mathbb {R}^n\) , \(n\geq 2\) be a bounded domain with boundary \(\partial G\) that is a smooth surface everywhere except at the origin \(\mathcal {O}\in \partial G\) , and near the point \(\mathcal {O}\) it is a conical surface with vertex at \(\mathcal {O}\) .