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In geometry, a enneahedron (or nonahedron) is a polyhedron with 9 faces. There are 2606 topologically distinct enneahedra〔Steven Dutch: (How Many Polyhedra are There? )〕 and none are regular, so this name is ambiguous. ==Examples== The most familiar enneahedra are the octagonal pyramid and the heptagonal prism. The heptagonal prism is a uniform polyhedron, with two regular heptagon faces and seven square faces. The octagonal pyramid has eight isosceles triangular faces around a regular octagonal base. Two more enneahedra are also found among the Johnson solids: the elongated square pyramid and the elongated triangular bipyramid. The three-dimensional associahedron, a near-miss Johnson solid with six pentagonal faces and three quadrilateral faces, is an enneahedron. Five Johnson solids have enneahedral duals: the triangular cupola, gyroelongated square pyramid, self-dual elongated square pyramid, triaugmented triangular prism (whose dual is the associahedron), and tridiminished icosahedron. Another enneahedron is the diminished trapezohedron with a square base, and 3 kite and 4 triangle faces. The Herschel graph also represents the vertices and edges of an enneahedron, with all of its faces quadrilaterals. It is the simplest polyhedron without a Hamiltonian cycle, the only enneahedron in which all faces have the same number of edges, and one of only three bipartite enneahedra. The two smallest isospectral polyhedral graphs are enneahedra with eight vertices each.〔.〕 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「enneahedron」の詳細全文を読む スポンサード リンク
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