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In geometry, a snub is an operation applied to a polyhedron. The term originates from Kepler's names of two Archimedean solids, for the snub cube (cubus simus) and snub dodecahedron (dodecaedron simum).〔Kepler, ''Harmonices Mundi'', 1619〕 In general, snubs have chiral symmetry with two forms, with clockwise or counterclockwise orientations. By Kepler's names, a snub can be seen as an expansion of a regular polyhedron, with the faces moved apart, and twists on their centers, adding new polygons centered on the original vertices, and pairs of triangles fitting between the original edges. The terminology was generalized by Coxeter, with a slightly different definition, for a wider set of uniform polytopes. == Conway snubs == John Conway explored generalized polyhedron operators, defining what is now called Conway polyhedron notation, which can be applied to polyhedra and tilings. Conway calls Coxeter's operation a ''semi-snub''.〔Conway, (2008) p.287 Coxeter's semi-snub operation〕 In this notation, snub is defined by the dual and gyro operators, as ''s'' = ''dg'', and it is equivalent to an alternation of a truncation of an ambo operator. Conway's notation itself avoids Coxeter's alternation (half) operation since it only applies for polyhedra with only even-sided faces. In 4-dimensions, Conway suggests the snub 24-cell should be called a ''semi-snub 24-cell'' because it doesn't represent an alternated omnitruncated 24-cell like his 3-dimensional polyhedron usage. It is instead actually an alternated truncated 24-cell.〔Conway, 2008, p.401 Gosset's Semi-snub Polyoctahedron〕 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「Snub (geometry)」の詳細全文を読む スポンサード リンク
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