Blas Herrera, Two conjectures of Victor Thebault linking tetrahedra with quadrics,
Forum Geometricorum, 15 (2015) 115--122.

Abstract. We prove two of Thebault's conjectures. The first (1949) links four lines, that they are rulings of hyperbolic paraboloids or that they are coplanar, with orthocentric or isodynamic tetrahedra, respectively. The second (1953) links the radical center of four spheres with elements of tetrahedra.

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