For a subset K \subseteq {\Bb R}^n and
E : = {\Bb R}^n \K we consider some operator
\sigma : {\cal P}(E) \rightarrow {\cal P}(E)
induced by visibility in a canonical way. If K
is compact and E is connected, we prove that K
is convex if and only if \sigma is a closure
operator.
Keywords :
convexity, closure operators, visibility, compact and convex body