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In his 1619 book Harmonices Mundi, Johannes Kepler observed the existence of the infinite family of antiprisms. [1] This has conventionally been thought of as the first discovery of these shapes, but they may have been known earlier: an unsigned printing block for the net of a hexagonal antiprism has been attributed to Hieronymus Andreae, who died in 1556.
Note that the pentagram face has an ambiguous interior because it is self-intersecting. The central pentagon region can be considered interior or exterior depending on how interior is defined. One definition of interior is the set of points that have a ray that crosses the boundary an odd number of times to escape the perimeter.
In geometry, the hexagonal antiprism is the 4th in an infinite set of antiprisms formed by an even-numbered sequence of triangle sides closed by two polygon caps. Antiprisms are similar to prisms except the bases are twisted relative to each other, and that the side faces are triangles, rather than quadrilaterals .
The regular octahedron can be considered as the antiprism, a prism like polyhedron in which lateral faces are replaced by alternating equilateral triangles. It is also called trigonal antiprism. [19] Therefore, it has the property of quasiregular, a polyhedron in which two different polygonal faces are alternating and meet at a vertex. [20]
If p/q is an integer, i.e. if q = 1, the prism or antiprism is convex. (The fraction is always assumed to be stated in lowest terms.) An antiprism with p/q < 2 is crossed or retrograde; its vertex figure resembles a bowtie. If p/q < 3/2 no uniform antiprism can exist, as its vertex figure would have to violate the triangle inequality.
In geometry, the heptagonal antiprism is the fifth in an infinite set of antiprisms formed by two parallel polygons separated by a strip of triangles. In the case of the heptagonal antiprism, the caps are two regular heptagons. As a result, this polyhedron has 14 vertices, and 14 equilateral triangle faces.
The apeirogonal tiling is the arithmetic limit of the family of prisms t{2, p} or p.4.4, as p tends to infinity, thereby turning the prism into a Euclidean tiling.. An alternation operation can create an apeirogonal antiprism composed of three triangles and one apeirogon at each vertex.