English

Rotation inside convex Kakeya sets

Metric Geometry 2022-11-03 v2 Combinatorics

Abstract

Let KK be a convex body (a compact convex set) in Rd\mathbb{R}^d, that contains a copy of another body SS in every possible orientation. Is it always possible to continuously move any one copy of SS into another, inside KK? As a stronger question, is it always possible to continuously select, for each orientation, one copy of SS in that orientation? These questions were asked by Croft. We show that, in two dimensions, the stronger question always has an affirmative answer. We also show that in three dimensions the answer is negative, even for the case when SS is a line segment -- but that in any dimension the first question has a positive answer when SS is a line segment. And we prove that, surprisingly, the answer to the first question is negative in dimension four for general SS.

Cite

@article{arxiv.2209.09728,
  title  = {Rotation inside convex Kakeya sets},
  author = {Barnabás Janzer},
  journal= {arXiv preprint arXiv:2209.09728},
  year   = {2022}
}

Comments

25 pages, 5 figures, updated introduction

R2 v1 2026-06-28T01:44:31.154Z