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.
Authors
- Hu Tan
- Ying Zhang (ORCID: https://orcid.org/0000-0002-2543-6818)
Institutions
- Chinese Academy of Sciences (CN)
- Soochow University (CN)
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