- Schläfli symbol
In

mathematics , the**Schläfli symbol**is a notation of the form {p,q,r,...} that definesregular polytope s andtessellations .The Schläfli symbol is named after the 19th-century mathematician

Ludwig Schläfli who made important contributions ingeometry and other areas.See also

list of regular polytopes .**Regular polygons (plane)**The Schläfli symbol of a regular

polygon with "n" edges is {"n"}.For example, a regular

pentagon is represented by {5}.See the convex

regular polygon and nonconvexstar polygon .For example, {5/2} is the

pentagram .**Regular polyhedra (3-space)**The Schläfli symbol of a regular

polyhedron is {"p","q"} if its faces are "p"-gons, and each vertex is surrounded by "q" faces (thevertex figure is a "q"-gon).For example {5,3} is the regular

dodecahedron . It has pentagonal faces, and 3 pentagons around each vertex.See the 5 convex

Platonic solid s, the 4 nonconvexKepler-Poinsot polyhedra .Schläfli symbols may also be defined for regular

tessellation s of Euclidean or hyperbolic space in a similar way.For example, the

Hexagonal tiling is represented by {6,3}.**Regular polychora (4-space)**The Schläfli symbol of a regular

polychoron is of the form {"p","q","r"}. It has {"p"} regular polygonal faces, {"p","q"} cells, {"q","r"} regular polyhedral vertex figures, and {"r"} regular polygonal edge figures.See the six convex regular and 10 nonconvex polychora.

For example, the

120-cell is represented by {5,3,3}. It is made ofdodecahedron cells {5,3}, and has 3 cells around each edge.There is also one regular tessellation of Euclidean 3-space: the

cubic honeycomb , with a Schläfli symbol of {4,3,4}, made of cubic cells, and 4 cubes around each edge.There are also 4 regular hyperbolic tessellations including {5,3,4}, the

Hyperbolic small dodecahedral honeycomb , which fills space withdodecahedron cells.**Higher dimensions**For higher dimensional

polytope s, the Schläfli symbol is defined recursively as {"p"_{1}, "p"_{2}, ..., "p"_{"n" − 1}} if the facets have Schläfli symbol {"p"_{1},"p"_{2}, ..., "p"_{"n" − 2}} and thevertex figure s have Schläfli symbol {"p"_{2},"p"_{3}, ..., "p"_{"n" − 1}}.Notice that a vertex figure of a facet of a polytope and a facet of a vertex figure of the same polytope are the same: {"p"

_{2},"p"_{3}, ..., "p"_{"n" − 2}}.There are only 3 regular polytopes in 5 dimensions and above: the

simplex , {3,3,3,...,3}; thecross-polytope , {3,3, ... ,3,4}; and thehypercube , {4,3,3,...,3}. There are no non-convex regular polytopes above 4 dimensions.**Dual polytopes**For dimension 2 or higher, every polytope has a dual.

If a polytope has Schläfli symbol {"p"

_{1},"p"_{2}, ..., "p"_{"n" − 1}} then its dual has Schläfli symbol {"p"_{"n" − 1}, ..., "p"_{2},"p"_{1}}.If the sequence is the same forwards and backwards, the polytope is "self-dual". Every regular polytope in 2 dimensions (polygon) is self-dual.

**Prismatic forms**Prismatic polytopes can be defined and named as a

Cartesian product of lower dimensional polytopes:

* A**p-gonal prism**, with vertex figure "p.4.4" as $egin\{Bmatrix\}\; end\{Bmatrix\}\; imes\; egin\{Bmatrix\}\; p\; end\{Bmatrix\}$.

* A uniform**{p,q}-hedral prism**as $egin\{Bmatrix\}\; end\{Bmatrix\}\; imes\; egin\{Bmatrix\}\; p,q\; end\{Bmatrix\}$.

* A uniform**p-q**as $egin\{Bmatrix\}\; p\; end\{Bmatrix\}\; imes\; egin\{Bmatrix\}\; q\; end\{Bmatrix\}$.duoprism A prism can also be represented as the truncation of a

hosohedron as $tegin\{Bmatrix\}\; 2,p\; end\{Bmatrix\}$, and anantiprism (snub hosohedron) as $segin\{Bmatrix\}\; 2\; \backslash \; p\; end\{Bmatrix\}$.**Extended Schläfli symbols for uniform polytopes**Uniform polytope s, made from aWythoff construction , are represented by an extended truncation notation from a regular form {p,q,...}. There are a number of parallel symbolic forms that reference the elements of the "Schläfli symbol", discussed by dimension below.**Uniform polyhedra and tilings**For polyhedra, one extended Schläfli symbol is used in the 1954 paper by Coxeter enumerating the paper tiled "uniform polyhedra".

Every regular polyhedron or tiling {p,q} has 7 forms, including the regular form and its dual, corresponding to positions within the fundamental right triangle. An 8th special form, the "snubs", correspond to an alternation of the omnitruncated form.

For instance, t{3,3} simply means

truncated tetrahedron .A second, more general notation, also used by Coxeter applies to all dimensions, and are specified by a

**t**followed by a list of indices corresponding toWythoff construction mirrors. (They also correspond to ringed nodes in aCoxeter-Dynkin diagram .)For example, the

truncated hexahedron can be represented by t_{0,1}{4,3} and it can be seen as midway between thecube , t_{0}{4,3}, and thecuboctahedron , t_{1}{4,3}.In each a Wythoff construction operational name is given first. Second some have alternate terminology (given in parentheses) apply only for a given dimension. Specifically omnitruncation and expansion, as well as dual relations apply differently in each dimension.

**Uniform polychora and honeycombs**There are up to 15 different truncation forms for polychora and honeycombs based on each {p,q,r} regular form.

See

uniform polychoron andconvex uniform honeycomb .The subscripted-t notation is parallel to the graphical

Coxeter-Dynkin diagram , with each graph node representing the 4 hyperplanes of the reflection mirrors in the fundamental domain.**References*** "The Beauty of Geometry: Twelve Essays" (1999), Dover Publications ISBN 978-0-486-40919-1 (Chapter 3: Wythoff's construction for uniform polytopes, p41-53)

* Johnson, N.W. "Uniform Polytopes", Manuscript (1991)

* Johnson, N.W. "The Theory of Uniform Polytopes and Honeycombs", Ph.D. Dissertation, University of Toronto, 1966

* Coxeter, H.S.M.; "Regular Polytopes", (Methuen and Co., 1948). (pp. 14, 69, 149)

* Coxeter, Longuet-Higgins, Miller, "Uniform polyhedra",**Phil. Trans.**1954, 246 A, 401-50. (Extended Schläfli notation defined: Table 1: p 403)**External links***

* [*http://bbs.sachina.pku.edu.cn/Stat/Math_World/math/w/w166.htm Wythoff Symbol and generalized Schläfli Symbols*]

* [*http://www.ac-noumea.nc/maths/amc/polyhedr/names_.htm polyhedral names et notations*]

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**Schläfli-Symbol**— Das Schläfli Symbol, benannt nach dem Schweizer Mathematiker Ludwig Schläfli, wird in der Form benutzt, um reguläre Polygone, Polyeder und andere Vielflächner, auch in höheren Dimensionen, zu beschreiben. Wenn p ganz ist, beschreibt das Symbol p… … Deutsch Wikipedia**Schläfli**— Ludwig Schläfli Ludwig Schläfli (* 15. Januar 1814 in Grasswil, heute zu Seeberg; † 20. März 1895 in Bern) war ein Schweizer Mathematiker der sich mit Geometrie und komplexer Analysis (damals Funktionentheorie g … Deutsch Wikipedia**Schläfli-Hess polychoron**— In four dimensional geometry, Schläfli Hess polychora are the complete set of 10 regular self intersecting star polychora (Four dimensional polytopes). They are named in honor of their discoverers: Ludwig Schläfli and Edmund Hess. They are all… … Wikipedia**Schläfli–Hess polychoron**— The great grand 120 cell, one of ten Schläfli–Hess polychora by orthographic projection. In four dimensional geometry, Schläfli–Hess polychora are the complete set of 10 regular self intersecting star polychora (four dimensional polytopes). They… … Wikipedia**Ludwig Schläfli**— (* 15. Januar 1814 in Grasswil, heute zu Seeberg; † 20. März 1895 in Bern) war ein Schweizer Mathematiker, der sich mit Geometrie und komplexer Analysis (damals Funktionentheorie g … Deutsch Wikipedia**Símbolo de Schläfli**— En geometría, el símbolo de Schläfli es una notación simple de la forma que proporciona un sumario de algunas propiedades importantes de un politopo regular o de una teselación (teselado o embaldosado) regular. Debe su nombre al matemático suizo… … Wikipedia Español**Ludwig Schläfli**— (15 January, 1814 ndash;1895) was a Swiss geometer and complex analyst (at the time called function theory) who was one of the key figures in developing the notion of higher dimensional spaces. The concept of multidimensionality has since come to … Wikipedia**Symbole de Schläfli**— En mathématiques, le symbole de Schläfli est une notation de la forme {p,q,r, …} qui permet de définir les polyèdres réguliers et les tessellations. Cette notation donne un résumé de certaines propriétés importantes d un polytope régulier… … Wikipédia en Français**Hexicated 7-cube**— Orthogonal projections in BC4 Coxeter plane 7 cube … Wikipedia**Hexicated 7-simplex**— 7 simplex … Wikipedia