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Semiregular polytope

From Wikipedia, the free encyclopedia
Isogonal polytope with regular facets
Gosset's figures
3D honeycombs

Simple tetroctahedric check

Complex tetroctahedric check
4D polytopes

Tetroctahedric

Octicosahedric

Tetricosahedric

Ingeometry, byThorold Gosset's definition asemiregular polytope is usually taken to be apolytope that isvertex-transitive and has all itsfacets beingregular polytopes.E.L. Elte compiled alonger list in 1912 asThe Semiregular Polytopes of the Hyperspaces which included a wider definition.

Gosset's list

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Inthree-dimensional space and below, the termssemiregular polytope anduniform polytope have identical meanings, because all uniformpolygons must beregular. However, since not alluniform polyhedra areregular, the number of semiregular polytopes in dimensions higher than three is much smaller than the number of uniform polytopes in the same number of dimensions.

The three convex semiregular4-polytopes are therectified 5-cell,snub 24-cell andrectified 600-cell. The only semiregular polytopes in higher dimensions are thek21 polytopes, where the rectified 5-cell is the special case ofk = 0. These were all listed by Gosset, but a proof of the completeness of this list was not published until the work ofMakarov (1988) for four dimensions, andBlind & Blind (1991) for higher dimensions.

Gosset's 4-polytopes (with his names in parentheses)
Rectified 5-cell (Tetroctahedric),
Rectified 600-cell (Octicosahedric),
Snub 24-cell (Tetricosahedric),, or
Semiregular E-polytopes in higher dimensions
5-demicube (5-ic semi-regular), a5-polytope,
221 polytope (6-ic semi-regular), a6-polytope, or
321 polytope (7-ic semi-regular), a7-polytope,
421 polytope (8-ic semi-regular), an8-polytope,

Euclidean honeycombs

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Thetetrahedral-octahedral honeycomb in Euclidean 3-space has alternating tetrahedral and octahedral cells.

Semiregular polytopes can be extended to semiregularhoneycombs. The semiregular Euclidean honeycombs are thetetrahedral-octahedral honeycomb (3D),gyrated alternated cubic honeycomb (3D) and the521 honeycomb (8D).

Gossethoneycombs:

  1. Tetrahedral-octahedral honeycomb oralternated cubic honeycomb (Simple tetroctahedric check), (Alsoquasiregular polytope)
  2. Gyrated alternated cubic honeycomb (Complex tetroctahedric check),

Semiregular E-honeycomb:

Gosset (1900) additionally allowed Euclidean honeycombs as facets of higher-dimensional Euclidean honeycombs, giving the following additional figures:

  1. Hypercubic honeycomb prism, named by Gosset as the (n – 1)-ic semi-check (analogous to a single rank or file of a chessboard)
  2. Alternated hexagonal slab honeycomb (tetroctahedric semi-check),

Hyperbolic honeycombs

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Thehyperbolic tetrahedral-octahedral honeycomb has tetrahedral and two types of octahedral cells.

There are also hyperbolic uniform honeycombs composed of only regular cells (Coxeter & Whitrow 1950), including:

See also

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References

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