Bianchi–Gruber conjecture on centrally symmetric sections

Let KRnK\subset\mathbb R^n, n3n\geq 3, be a strictly convex body, and let S\mathcal S be a family of hyperplanes that is the image of an embedding of the tangent bundle of the sphere Sn1\mathbb S^{n-1}, with every hyperplane in S\mathcal S intersecting the interior of KK. Bianchi–Gruber conjecture. If every such intersection is centrally symmetric and, with possibly a few exceptions, does not contain a possibly existing center of symmetry of KK, then KK is an ellipsoid. The conjecture is known under the stronger assumption that all the sections are ellipsoids, while the stated version remains open.

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Primary source

Bartłomiej Zawalski, “On flat shadow boundaries from point light sources and the characterization of ellipsoids”, arXiv:2603.29130 (2026).

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