English

A reduced planar body with area greater than $πΔ^2/4$

Metric Geometry 2026-06-26 v1 Computational Geometry Combinatorics

Abstract

We construct a reduced planar convex body RR with thickness Δ(R)=1\Delta(R)=1 and area(R)=0.786215>0.785398=π4.\operatorname{area}(R)=0.786215\ldots>0.785398\ldots=\frac{\pi}{4}. Thus RR is a counterexample to Lassak's conjectured upper bound area(π/4)Δ2\operatorname{area}\le(\pi/4)\Delta^2 for planar reduced bodies. The construction is given by an explicit support function, and the proofs use only elementary support-function, width, area, and contact-point computations.

Keywords

Cite

@article{arxiv.2606.28612,
  title  = {A reduced planar body with area greater than $πΔ^2/4$},
  author = {Scott Duke Kominers},
  journal= {arXiv preprint arXiv:2606.28612},
  year   = {2026}
}

Comments

10 pages, 2 figures, plus verification source code