¶ Invisible Tetrahedron
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Index Entry
Invisible Tetrahedron:
“Descartes discovered the 720° but he didn’t call it the tetrahedron. [cf. Letter from Coxeter, 30 Oct. '70.] The tetrahedron can be turned inside out; it can become invisible. There is an internal invisible tetrahedron of concave angles, 720° or less.”
¶ Citations
- RBF to EJA, Blackstone Hotel, Chicago, 31 May 1971
