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2504.04525

Hausdorff measure of dominated planar self-affine sets with large dimension

Balázs Bárány

correctmedium confidence
Category
Not specified
Journal tier
Strong Field
Processed
Sep 28, 2025, 12:56 AM

Audit review

The paper’s Theorem 1.1 states and proves the equivalence (a)⇔(b)⇔(c)⇔(d) for dominated planar self‑affine IFS with affinity dimension s0∈(1,2], using (i) a self‑affine ‘reverse slicing’ inequality (Lemma 3.1) to get (a)⇒(b), (ii) a Perron–Frobenius/transfer‑operator framework to obtain the dichotomy (b)⇔(c), and (iii) a representation of π∗μK via slice integrals (Proposition 2.4) to get (c)⇒(d), followed by the mass distribution principle for (d)⇒(a) (see Theorem 1.1 and its proof outline in the PDF, together with Lemma 3.1 and Propositions 2.1–2.4: ). By contrast, the candidate solution makes several overstrong and incorrect claims. Most notably, it asserts a uniform “thin‑rectangle” slicing lower bound c·∑|ι|=nφs0(Aι) ≤ ∫H∞s0−1(X∩proj−1V(t))dt which, together with the Gibbs property, would force the slice integral to be positive for every dominated system, contradicting examples with Hs0(X)=0 (e.g., Example 1.1 in the paper: ). It further claims a 1‑Frostman bound for (projV)∗π∗μK for all V∈XF without assuming Hs0(X)>0, whereas the paper shows this bound only as a consequence of Hs0(X)>0 (Theorem 1.2(i): and its proof ), and explicitly remarks on the difficulty of proving it in general (). The model’s Step 1 geometry is also misstated (axes “within a fixed angle of every V∈XF”). Therefore, the paper’s argument is correct and internally consistent, while the model’s solution contains substantive errors.

Referee report (LaTeX)

\textbf{Recommendation:} minor revisions

\textbf{Journal Tier:} strong field

\textbf{Justification:}

The manuscript establishes a clean and conceptually satisfying characterisation of when the Hausdorff measure at the affinity dimension is positive for dominated planar self-affine sets. The combination of a self-affine reverse slicing inequality with a Perron–Frobenius operator approach is elegant and, to my knowledge, novel in this form. The results connect geometric measure properties (slice contents, Frostman bounds) with thermodynamic formalism, and the consequences (e.g., one-dimensional projection bounds when H\^{s0}(X)>0) are of independent interest. Exposition is generally clear; a few statements could benefit from additional intuition and cross-references.