Bianchi–Gruber conjecture on centrally symmetric sections
Let , , be a strictly convex body, and let be a family of hyperplanes that is the image of an embedding of the tangent bundle of the sphere , with every hyperplane in intersecting the interior of . 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 , then is an ellipsoid. The conjecture is known under the stronger assumption that all the sections are ellipsoids, while the stated version remains open.
References
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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