Canonical bijection between degenerate tetrahedra and planar quadruples
Canonical bijection between degenerate tetrahedra and planar quadruples
A quadruple of points in the special affine plane determines triangle and Varignon-parallelogram areas. Consider the corresponding quadruple of Euclidean-plane points for which the radius of gyration attains its unique minimum subject to preserving those areas. Let degenerate tetrahedra be the tetrahedra defined by the zeros of . Canonical-bijection conjecture. The bijection between affine-plane quadruples and the corresponding minimizing Euclidean-plane quadruples extends to a bijection between the set of degenerate tetrahedra and the set of all quadruples in the Euclidean plane; moreover, this mapping is, or can be chosen to be, canonical, so that the two sets can be identified.
Sources & referencesView supporting material
Primary source
Timothy F. Havel, “An Extension of Heron's Formula to Tetrahedra, and the Projective Nature of Its Zeros”, arXiv:2204.08089 (2025).
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