English

How to avoid a compact set

Logic 2017-07-18 v2 Metric Geometry

Abstract

A first-order expansion of the R\mathbb{R}-vector space structure on R\mathbb{R} does not define every compact subset of every Rn\mathbb{R}^n if and only if topological and Hausdorff dimension coincide on all closed definable sets. Equivalently, if ARkA \subseteq \mathbb{R}^k is closed and the Hausdorff dimension of AA exceeds the topological dimension of AA, then every compact subset of every Rn\mathbb{R}^n can be constructed from AA using finitely many boolean operations, cartesian products, and linear operations. The same statement fails when Hausdorff dimension is replaced by packing dimension.

Keywords

Cite

@article{arxiv.1612.00785,
  title  = {How to avoid a compact set},
  author = {Antongiulio Fornasiero and Philipp Hieronymi and Erik Walsberg},
  journal= {arXiv preprint arXiv:1612.00785},
  year   = {2017}
}
R2 v1 2026-06-22T17:12:00.606Z