a set of tetrahedral dice. Especially in roleplaying, this solid is known as a 4-sided die, one of the more common polyhedral dice, with the number rolled appearing around the bottom or on the top vertex. Some Rubik's Cube-like puzzles are tetrahedral, such as the Pyraminx and Pyramorphix. Geology The tetrahedral hypothesis, originally published by William Lowthian Green to explain the formation of the Earth, was popular through the early 20th century. Popular culture Stanley Kubrick originally intended the monolith in 2001: A Space Odyssey to be a tetrahedron, according to Marvin Minsky, a cognitive scientist and expert on artificial intelligence who advised Kubrick on the HAL 9000 computer and other aspects of the movie. Kubrick scrapped the idea of using the tetrahedron as a visitor who saw footage of it did not recognize what it was and he did not want anything in the movie regular people did not understand. Tetrahedral graph The skeleton of the tetrahedron (comprising the vertices and edges) forms a graph, with 4 vertices, and 6 edges. It is a special case of the complete graph, K4, and wheel graph, W4. It is one of 5 Platonic graphs, each a skeleton of its Platonic solid. See also Boerdijk–Coxeter helix Möbius configuration Caltrop Demihypercube and simplex – n-dimensional analogues Pentachoron – 4-dimensional analogue Synergetics (Fuller) Tetrahedral kite Tetrahedral number Tetrahedron packing Triangular dipyramid – constructed by joining two tetrahedra along one face Trirectangular tetrahedron Orthoscheme Notes References Bibliography External links Free paper models of a tetrahedron and many other polyhedra An Amazing, Space Filling, Non-regular Tetrahedron that also includes a description of a "rotating ring of tetrahedra", also known as a kaleidocycle. Deltahedra Platonic solids Individual graphs Self-dual polyhedra Prismatoid polyhedra Pyramids and bipyramids