Banaji–Fraser conjecture on characterizing Hausdorff dimension by Hölder stability

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Let nn be a positive integer, let K(Rn)\mathcal{K}(\mathbb{R}^n) denote the compact subsets of Rn\mathbb{R}^n, and let dim⁡ ⁣:K(Rn)→[0,n]\dim\colon\mathcal{K}(\mathbb{R}^n)\to[0,n] be a dimension. Assume that it agrees with the similarity dimension on each self-similar set satisfying the strong separation condition; is monotone, meaning that A⊂BA\subset B implies dim⁡A≤dim⁡B\dim A\leq\dim B; is σ\sigma-stable, meaning that

dim⁡(⋃i=1∞Ai)=sup⁡idim⁡Ai;\dim\left(\bigcup_{i=1}^{\infty}A_i\right)=\sup_i\dim A_i;

is a Borel function; and is Hölder-stable, meaning that for every α∈(0,1]\alpha\in(0,1] and every α\alpha-Hölder map f ⁣:Rn→Rnf\colon\mathbb{R}^n\to\mathbb{R}^n,

dim⁡f(A)≤1αdim⁡A.\dim f(A)\leq\frac{1}{\alpha}\dim A.

Banaji–Fraser conjecture. Under these assumptions, dim⁡\dim is the Hausdorff dimension. This proposes that adding Hölder stability to the standard properties of a dimension characterizes Hausdorff dimension, in contrast with the negative answer obtained for the corresponding question without Hölder stability. The source does not provide a resolution of this modified question.

References

Primary source

Richárd Balka and Tamás Keleti, “New Hausdorff type dimensions and optimal bounds for bilipschitz invariant dimensions”, arXiv:2312.06456 (2026).

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