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Fig. 470.02A Role of Tetrahedra and Octahedra in Vector Equilibrium: A. Positive-negative tetrahedron system. B. Vector equilibrium formed by four positive-negative tetrahedron systems with common central vertex and coinciding radial edges. Equilibrium of system results from positive-negative action of double radial vectors. C. The relationship of space-filling tetrahedra and octahedra to the vector equilibrium defined by eight radially disposed tetrahedra.