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arXiv · 2610.29809

A bounded Borel set in the plane none of whose orthogonal projections is Borel

Dmitrii Krokhalev
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Abstract

We construct a bounded Borel set in the plane whose orthogonal projection onto every line is non-Borel. This gives a negative answer to a question of Thierry De Pauw.

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Dmitrii Krokhalev. 2026-10-21. A bounded Borel set in the plane none of whose orthogonal projections is Borel. https://arxiv.org/abs/2610.29809

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