Counterexamples to the Knaster problem in all remaining dimensions

We construct counterexamples to Knaster's 1947 problem in all remaining cases. For every ambient dimension n ≥ 4, we obtain a real polynomial on R^{n} and n linearly independent points on S^{n-1} whose values cannot be equalized by any orthogonal transformation. These examples settle the remaining cases with target dimension m = 1 and, together with earlier results, complete the determination of the parameters in the original problem. The construction begins with a stronger four-point theorem on every sphere S^{n-1}, n ≥ 2. Its main ingredient is a suspension theorem that extends Karasev's local obstruction to arbitrary dimension by preserving a differential condition for an even function and an odd function. A uniform Taylor estimate yields finite configurations, and stability under perturbation gives the polynomial examples. The four-point theorem also disproves the uniform weak Knaster conjecture for real-valued functions.

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Publication Details

Journal
Zenodo (CERN European Organization for Nuclear Research)
Published
2026-10-04
DOI
https://doi.org/10.5281/zenodo.23140752
Primary Topic
Advanced Combinatorial Mathematics
Type
preprint
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preprint

Counterexamples to the Knaster problem in all remaining dimensions

Hu Tan, Ying Zhang
Zenodo (CERN European Organization for Nuclear Research)
Advanced Combinatorial Mathematics
preprint

Counterexamples to the Knaster problem in all remaining dimensions

Hu Tan, Ying Zhang
preprint en

Abstract

We construct counterexamples to Knaster's 1947 problem in all remaining cases. For every ambient dimension n ≥ 4, we obtain a real polynomial on R^{n} and n linearly independent points on S^{n-1} whose values cannot be equalized by any orthogonal transformation. These examples settle the remaining cases with target dimension m = 1 and, together with earlier results, complete the determination of the parameters in the original problem. The construction begins with a stronger four-point theorem on every sphere S^{n-1}, n ≥ 2. Its main ingredient is a suspension theorem that extends Karasev's local obstruction to arbitrary dimension by preserving a differential condition for an even function and an odd function. A uniform Taylor estimate yields finite configurations, and stability under perturbation gives the polynomial examples. The four-point theorem also disproves the uniform weak Knaster conjecture for real-valued functions.

Zenodo (CERN European Organization for Nuclear Research)
Chinese Academy of Sciences (CN), Soochow University (CN)
Advanced Combinatorial Mathematics
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Counterexamples to the Knaster problem in all remaining dimensions — Hu Tan, Ying Zhang · Zenodo (CERN European Organization for Nuclear Research) (2026) | TGRS Research Map | TGRS