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Remove the lower density assumption from the main theorem

Ascertain whether Theorem 1.1 (Theorem \ref{th:main}) remains valid without assuming positive lower p-density almost everywhere; specifically, determine if for any compact metric space (X,d) with 0 < H^p(X) < ∞ that is not p-rectifiable, there still exists a positive-measure subset F ⊂ X, a metric space (Y,d), and a Lipschitz map f: F → Y such that H^p_d(f(F)) > 0 and f has no biLipschitz restriction on any positive-measure subset of F, even when the hypothesis θ_*^p(X,x) > 0 almost everywhere is removed.

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Background

The main theorem (Theorem \ref{th:main}) requires that the space has positive lower p-density almost everywhere to construct a Lipschitz map with positive-measure image and no positive-measure biLipschitz pieces. The authors indicate the lower density is used at a specific point (via equation (\ref{eq:Fr-defn}) in proving Lemma \ref{l:not-bilip}).

They ask whether the theorem’s conclusion still holds without this density hypothesis, which would broaden the applicability of their characterization.

References

The only place we use the lower density assumption is in the application of eq:Fr-defn in the proof of Lemma \ref{l:not-bilip}. We thus also ask if the lower density assumption is necessary. Is Theorem \ref{th:main} still true if one removes the $\cHp$ almost everywhere $\theta_*p(X,x) > 0$ hypothesis?

Characterizing rectifiability via biLipschitz pieces of Lipschitz mappings on the space (2510.13525 - Li et al., 15 Oct 2025) in Introduction (Problem)