Countable-exceptional-set conjecture for projections of planar self-similar sets

Let KK be a self-similar set in the plane, and call a direction πG(2,1)\pi\in G(2,1) exceptional for orthogonal projections of KK if the projection dimension equality does not hold. Countable-exceptional-set conjecture. For any self-similar set in the plane, the exceptional set is at most countable and explicitly determinable. This conjecture strengthens Marstrand's theorem by predicting that the exceptional directions for planar self-similar sets are not merely a null set but countable and explicitly identifiable. When the self-similar construction involves irrational rotations, the conjecture was confirmed by Peres and Shmerkin; the parser reports the conjecture as resolved.

Sources & referencesView supporting material

Primary source

Meng Wu, “Projection theorems with countably many exceptions and applications to the exact overlaps conjecture”, arXiv:2503.21923 (2025).

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