Equichordal projection conjecture for a point

Let KR3K\subset\mathbb R^3 be a convex body and let pp be a point in its interior. For uS2u\in\mathbb S^2, let πu\pi_u denote orthogonal projection in direction uu. Point equichordal projection conjecture. If, for every uS2u\in\mathbb S^2, the point πu(p)\pi_u(p) is an equichordal point of πu(K)\pi_u(K), then KK is a ball. This is the point-inner-body case suggested after the projected-body result, and the paper indicates that a subsequent theorem provides partial progress toward a proof. The conjecture remains open.

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Primary source

Victor A. Aguilar-Arteaga, Rafael Iván Ayala-Figueroa, Jesús Jerónimo-Castro and Efrén Morales-Amaya, “An equichordal characterization of the ellipsoid and the sphere”, arXiv:2308.02956 (2026).

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