Über die Erzeugung konvexer Polygone in der projektiven Ebene (Q1060707)

In the real projective plane \(\Pi\) a subset X is called \(\Pi\)-convex if for any two distinct points x,y\(\in X\) at least one of the two segments with endpoints x and y is contained in X. To any subset X of \(\Pi\) one can define a \(\Pi\)-convex hull as a smallest \(\Pi\)-convex set containing X; this is in general not unique. The author proves some results which can be viewed as an analogue of the fact that in the Euclidean plane any convex polygon is the convex hull of its extreme points.