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Paper Referee

Every Four-Dimensional Kakeya Set Has Full Hausdorff Dimension

OpenAI preprintReviewed version: September 24, 2026

Findings and severity labels come from OSVerify’s internal review and do not necessarily establish that the paper’s main theorem is false.

Major issues 0

No major issues were released in this report.

Minor issues 2

Minor · Issue 01Link

The weighted plank estimate has the wrong lemma number

Where the issue occurs

Section 1.1, paragraph introducing the three-dimensional weighted plank input · p. 4

The three-dimensional estimate used in our reduction is the weighted full-time plank bound of OpenAI [24, Lemma 2.3], recorded as Lemma 2.15.

This first citation should point to Lemma 3.3 in reference [24].

Section 2.5, proof of Lemma 2.15, first sentence · p. 18

This is the indexed weighted formulation of OpenAI [24, Lemma 2.3].

The same incorrect external lemma number is repeated here.

Section 5.1, proof of Lemma 5.1, weighted full-trace application · p. 72

Apply Lemma 2.15, namely the weighted full-trace form of OpenAI [24, Lemma 2.3].

This third citation also needs Lemma 3.3.

References, entry [24], final note · p. 175

Lemma 2.3.

The bibliography note repeats the same incorrect locator.

Issue & evidence

The cited September 23, 2026 preprint states the weighted plank estimate as Lemma 3.3 on page 20; item 2.3 is instead the critical-exponent definition. The incorrect locator appears in the four passages quoted above. The intended lemma's statement matches the weighted plank input.

Proposed repair by OSVerify

Replace Lemma~2.3 with Lemma~3.3 in the three citations to ThreeDimensional and its bibliography note. This corrects the reference without altering the stated weighted plank estimate.

Related context
  • Background Section 2.5, proof of Lemma 2.15 (Weighted full-time plank estimate)

    This is the paper’s own formulation of the imported estimate. The reported defect is the locator in reference [24], not the stated weighted estimate.

Minor · Issue 02Link

The Jacobian sentence reverses the coordinate maps

Where the issue occurs

Section 4.3, proof of Proposition 4.7, sentence immediately before Equation (4.20) · p. 56

The map to unit base coordinates u of Qs has Jacobian qs Js; denote this map by baseQ.

This sentence attaches the inverse map’s Jacobian to the parent-to-unit map. The displayed density estimate (4.20) already has the correct factor.

Issue & evidence

The Jacobian sentence preceding (4.20) reverses the coordinate maps. The parent-to-unit coordinate map base_Q has absolute Jacobian (q_sJ_s)⁻¹; q_sJ_s belongs to its inverse. The displayed pushforward density estimate uses the correct change-of-variables factor.

Proposed repair by OSVerify

Replace the Jacobian sentence with: “Writing u = base_Q(t,y) for unit base coordinates, the volume elements satisfy dt dy = q_sJ_s du.” Keep (4.20) and the following time-normalization formulas unchanged; their change-of-variables factors are already correct.

Related context
  • Background Section 2.3, Definition 2.8 and Equation (2.7); Section 2.4, proof of Lemma 2.13

    Defines the spatial chart determinant and the inverse affine change of coordinates used to check the direction of the Jacobian.

  • Background Section 2.4, Equation (2.15)

    Displays the corresponding density transformation, which agrees with the factor used later.

  • Downstream use Section 4.3, Equation (4.20) and following time normalization

    These formulas remain unchanged under the proposed sentence correction.