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On empty convex polygons in a planar point set. (English) Zbl 1088.52500
Summary: Let \(P\) be a set of \(n\) points in general position in the plane. Let \(X_{k}(P)\) denote the number of empty convex \(k\)-gons determined by \(P\).
We derive, using elementary proof techniques, several equalities and inequalities involving the quantities \(X_{k}(P)\) and several related quantities. Most of these equalities and inequalities are new, except for a few that have been proved earlier using a considerably more complex machinery from matroid and polytope theory, and algebraic topology. Some of these relationships are also extended to higher dimensions. We present several implications of these relationships, and discuss their connection with several long-standing open problems, the most notorious of which is the existence of an empty convex hexagon in any point set with sufficiently many points.

52A10 Convex sets in \(2\) dimensions (including convex curves)
52A40 Inequalities and extremum problems involving convexity in convex geometry
Full Text: DOI
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