Circles and crossing planar compact convex sets
Abstract
Let be a compact convex subset of the plane , and assume that whenever is congruent to , then and are not crossing in a natural sense due to L. Fejes-T\'oth. A theorem of L. Fejes-T\'oth from 1967 states that the assumption above holds for if and only if is a disk. In a paper appeared in 2017, the present author introduced a new concept of crossing, and proved that L. Fejes-T\'oth's theorem remains true if the old concept is replaced by the new one. Our purpose is to describe the hierarchy among several variants of the new concepts and the old concept of crossing. In particular, we prove that each variant of the new concept of crossing is more restrictive then the old one. Therefore, L. Fejes-T\'oth's theorem from 1967 becomes an immediate consequence of the 2017 characterization of circles but not conversely. Finally, a mini-survey shows that this purely geometric paper has precursor in combinatorics and, mainly, in lattice theory.
Cite
@article{arxiv.1802.06457,
title = {Circles and crossing planar compact convex sets},
author = {Gábor Czédli},
journal= {arXiv preprint arXiv:1802.06457},
year = {2018}
}
Comments
14 pages, 9 figures