Reducing the upper bound for the Borsuk number in $\mathbb{R}^4$ to 8

Fuente: arXiv
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Autores principales: Tolmachev, Alexander, Voronov, Vsevolod
Formato: Preprint
Publicado: 2026
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author Tolmachev, Alexander
Voronov, Vsevolod
author_facet Tolmachev, Alexander
Voronov, Vsevolod
contents The Borsuk number $b(n)$ of $n$-dimensional Euclidean space $\mathbb{R}^n$ is the smallest integer such that any set $F \subset \mathbb{R}^n$ of unit diameter can be partitioned into $b(n)$ subsets of strictly smaller diameter. For $n=4$, the best known upper bound $b(4) \leq 9$ follows from a construction by M. Lassak (1982). In the present paper, we construct partitions of several variants of the truncated Lassak cover into 8 parts of diameter less than 1, thereby showing that $b(4) \leq 8$.
format Preprint
id arxiv_https___arxiv_org_abs_2605_19068
institution arXiv
publishDate 2026
record_format arxiv
spellingShingle Reducing the upper bound for the Borsuk number in $\mathbb{R}^4$ to 8
Tolmachev, Alexander
Voronov, Vsevolod
Metric Geometry
52C17, 52C10
The Borsuk number $b(n)$ of $n$-dimensional Euclidean space $\mathbb{R}^n$ is the smallest integer such that any set $F \subset \mathbb{R}^n$ of unit diameter can be partitioned into $b(n)$ subsets of strictly smaller diameter. For $n=4$, the best known upper bound $b(4) \leq 9$ follows from a construction by M. Lassak (1982). In the present paper, we construct partitions of several variants of the truncated Lassak cover into 8 parts of diameter less than 1, thereby showing that $b(4) \leq 8$.
title Reducing the upper bound for the Borsuk number in $\mathbb{R}^4$ to 8
topic Metric Geometry
52C17, 52C10
url https://arxiv.org/abs/2605.19068