If $S \subseteq R^n$ is compact and star-shaped, we consider a fixed, nonempty, compact and convex subset K of the convex kernel of S. We prove that $\sigma(sol=S\backslash K$, where $\sigma : \rho(R^n \backslash K) \rightarrow \rho(R^n \backslash T)$ denotes same closure operator induced by visibility problems, and so denotes the - appropriately defined - set of extreme points of S modula K