Variations on a theme of empty polytopes

Abstract

Given a set $S \subseteq \mathbb{R}^d$, an empty polytope has vertices in $S$ but contains no other point of $S$. Empty polytopes are closely related to so-called Helly numbers, which extend Helly's theorem to more general point sets in $\mathbb{R}^d$. We improve bounds on the number of vertices in empty polytopes in exponential lattices, arithmetic congruence sets, and 2-syndetic sets. We also study hollow polytopes, which have vertices in $S$ and no points of $S$ in their interior. We obtain bounds on the number of vertices in hollow polytopes under certain conditions, such as the vertices being in general position. Finally, we obtain relatively tight asymptotic bounds for polytopes which do not contain lattice segments of large length.