Applications of equidistant supporting surfaces of a convex body in the hyperbolic space

Abstract

For a hyperplane $H$ supporting a convex body $C$ in the hyperbolic space ${\mathbb{H}}^d$ we define the width of $C$ determined by $H$ as the distance between $H$ and a most distant ultraparallel hyperplane supporting $C$. The thickness (i.e., the minimum width) of $C$ is denoted by $\Delta (C)$. A convex body $R\subset {\mathbb{H}}^d$ is called reduced if for every body $Z⊊R$ we have $\Delta (Z)<\Delta (R)$. We show that for any extreme point $e$ of a reduced body $R\subset {\mathbb{H}}^d$ there exists a supporting hyperplane $H$ of $R$ which passes through $e$ or its equidistant surface supporting $R$ passes through $e$. Bodies of constant width in ${\mathbb{H}}^d$ are defined as bodies whose all widths are equal. We prove that every complete body in ${\mathbb{H}}^d$ is a body of constant width.

7 pages. arXiv admin note: text overlap with arXiv:2401.07831