
In
geometry
Geometry (; ) is, with arithmetic, one of the oldest branches of mathematics. It is concerned with properties of space such as the distance, shape, size, and relative position of figures. A mathematician who works in the field of geometry is c ...
of 4 dimensions or higher, a double prism or duoprism is a
polytope resulting from the
Cartesian product
In mathematics, specifically set theory, the Cartesian product of two sets ''A'' and ''B'', denoted ''A''×''B'', is the set of all ordered pairs where ''a'' is in ''A'' and ''b'' is in ''B''. In terms of set-builder notation, that is
: A\ti ...
of two polytopes, each of two dimensions or higher. The Cartesian product of an -polytope and an -polytope is an -polytope, where and are dimensions of 2 (
polygon
In geometry, a polygon () is a plane figure that is described by a finite number of straight line segments connected to form a closed ''polygonal chain'' (or ''polygonal circuit''). The bounded plane region, the bounding circuit, or the two toge ...
) or higher.
The lowest-dimensional duoprisms exist in
4-dimensional space
A four-dimensional space (4D) is a mathematical extension of the concept of three-dimensional or 3D space. Three-dimensional space is the simplest possible abstraction of the observation that one only needs three numbers, called ''dimensions'', ...
as
4-polytope
In geometry, a 4-polytope (sometimes also called a polychoron, polycell, or polyhedroid) is a four-dimensional polytope. It is a connected and closed figure, composed of lower-dimensional polytopal elements: vertices, edges, faces (polygons), an ...
s being the Cartesian product of two polygons in 2-dimensional
Euclidean space
Euclidean space is the fundamental space of geometry, intended to represent physical space. Originally, that is, in Euclid's Elements, Euclid's ''Elements'', it was the three-dimensional space of Euclidean geometry, but in modern mathematics ther ...
. More precisely, it is the
set
Set, The Set, SET or SETS may refer to:
Science, technology, and mathematics Mathematics
*Set (mathematics), a collection of elements
*Category of sets, the category whose objects and morphisms are sets and total functions, respectively
Electro ...
of points:
:
where and are the sets of the points contained in the respective polygons. Such a duoprism is
convex if both bases are convex, and is bounded by
prismatic cells.
Nomenclature
Four-dimensional duoprisms are considered to be prismatic 4-polytopes. A duoprism constructed from two
regular polygons of the same edge length is a uniform duoprism.
A duoprism made of ''n''-polygons and ''m''-polygons is named by prefixing 'duoprism' with the names of the base polygons, for example: a ''triangular-pentagonal duoprism'' is the Cartesian product of a triangle and a pentagon.
An alternative, more concise way of specifying a particular duoprism is by prefixing with numbers denoting the base polygons, for example: 3,5-duoprism for the triangular-pentagonal duoprism.
Other alternative names:
* q-gonal-p-gonal prism
* q-gonal-p-gonal double prism
* q-gonal-p-gonal hyperprism
The term ''duoprism'' is coined by George Olshevsky, shortened from ''double prism''.
John Horton Conway proposed a similar name
proprism for ''product prism'', a Cartesian product of two or more polytopes of dimension at least two. The duoprisms are proprisms formed from exactly two polytopes.
Example 16-16 duoprism
Geometry of 4-dimensional duoprisms
A 4-dimensional
uniform
A uniform is a variety of clothing worn by members of an organization while participating in that organization's activity. Modern uniforms are most often worn by armed forces and paramilitary organizations such as police, emergency services, se ...
duoprism is created by the product of a regular ''n''-sided
polygon
In geometry, a polygon () is a plane figure that is described by a finite number of straight line segments connected to form a closed ''polygonal chain'' (or ''polygonal circuit''). The bounded plane region, the bounding circuit, or the two toge ...
and a regular ''m''-sided polygon with the same edge length. It is bounded by ''n'' ''m''-gonal
prisms and ''m'' ''n''-gonal prisms. For example, the Cartesian product of a triangle and a hexagon is a duoprism bounded by 6 triangular prisms and 3 hexagonal prisms.
*When ''m'' and ''n'' are identical, the resulting duoprism is bounded by 2''n'' identical ''n''-gonal prisms. For example, the Cartesian product of two triangles is a duoprism bounded by 6 triangular prisms.
*When ''m'' and ''n'' are identically 4, the resulting duoprism is bounded by 8 square prisms (
cubes
In geometry, a cube is a three-dimensional solid object bounded by six square faces, facets or sides, with three meeting at each vertex. Viewed from a corner it is a hexagon and its net is usually depicted as a cross.
The cube is the only r ...
), and is identical to the
tesseract.
The ''m''-gonal prisms are attached to each other via their ''m''-gonal faces, and form a closed loop. Similarly, the ''n''-gonal prisms are attached to each other via their ''n''-gonal faces, and form a second loop perpendicular to the first. These two loops are attached to each other via their square faces, and are mutually perpendicular.
As ''m'' and ''n'' approach infinity, the corresponding duoprisms approach the
duocylinder. As such, duoprisms are useful as non-
quadric approximations of the duocylinder.
Nets
Perspective projections
A cell-centered perspective projection makes a duoprism look like a
torus
In geometry, a torus (plural tori, colloquially donut or doughnut) is a surface of revolution generated by revolving a circle in three-dimensional space about an axis that is coplanar with the circle.
If the axis of revolution does not tou ...
, with two sets of orthogonal cells, p-gonal and q-gonal prisms.
The p-q duoprisms are identical to the q-p duoprisms, but look different in these projections because they are projected in the center of different cells.
Orthogonal projections
Vertex-centered orthogonal projections of p-p duoprisms project into
nsymmetry for odd degrees, and
for even degrees. There are n vertices projected into the center. For 4,4, it represents the A
3 Coxeter plane of the
tesseract. The 5,5 projection is identical to the 3D
rhombic triacontahedron.
Related polytopes

The
regular skew polyhedron
In geometry, the regular skew polyhedra are generalizations to the set of regular polyhedra which include the possibility of nonplanar faces or vertex figures. Coxeter looked at skew vertex figures which created new 4-dimensional regular polyhedra ...
, , exists in 4-space as the n
2 square faces of a ''n-n duoprism'', using all 2n
2 edges and n
2 vertices. The 2''n'' ''n''-gonal faces can be seen as removed. (skew polyhedra can be seen in the same way by a n-m duoprism, but these are not ''regular''.)
Duoantiprism

Like the
antiprisms as alternated
prism
Prism usually refers to:
* Prism (optics), a transparent optical component with flat surfaces that refract light
* Prism (geometry), a kind of polyhedron
Prism may also refer to:
Science and mathematics
* Prism (geology), a type of sedimentary ...
s, there is a set of 4-dimensional duoantiprisms:
4-polytopes
In geometry, a 4-polytope (sometimes also called a polychoron, polycell, or polyhedroid) is a four-dimensional polytope. It is a connected and closed figure, composed of lower-dimensional polytopal elements: vertices, edges, faces (polygons), an ...
that can be created by an
alternation operation applied to a duoprism. The alternated vertices create nonregular tetrahedral cells, except for the special case, the ''4-4 duoprism'' (
tesseract) which creates the uniform (and regular)
16-cell
In geometry, the 16-cell is the regular convex 4-polytope (four-dimensional analogue of a Platonic solid) with Schläfli symbol . It is one of the six regular convex 4-polytopes first described by the Swiss mathematician Ludwig Schläfli in the mi ...
. The 16-cell is the only convex uniform duoantiprism.
The duoprisms , t
0,1,2,3, can be alternated into , ht
0,1,2,3, the "duoantiprisms", which cannot be made uniform in general. The only convex uniform solution is the trivial case of p=q=2, which is a lower symmetry construction of the
tesseract , t
0,1,2,3, with its alternation as the
16-cell
In geometry, the 16-cell is the regular convex 4-polytope (four-dimensional analogue of a Platonic solid) with Schläfli symbol . It is one of the six regular convex 4-polytopes first described by the Swiss mathematician Ludwig Schläfli in the mi ...
, , ss.
The only nonconvex uniform solution is p=5, q=5/3, ht
0,1,2,3, , constructed from 10
pentagonal antiprisms, 10
pentagrammic crossed-antiprism
In geometry, the pentagrammic crossed-antiprism is one in an infinite set of nonconvex antiprisms formed by triangle sides and two regular star polygon caps, in this case two pentagrams.
It differs from the pentagrammic antiprism by having oppos ...
s, and 50 tetrahedra, known as the
great duoantiprism
In geometry, the great duoantiprism is the only uniform star-duoantiprism solution in 4-dimensional geometry. It has Schläfli symbol or Coxeter diagram , constructed from 10 pentagonal antiprisms, 10 pentagrammic crossed-antiprisms, and 50 ...
(gudap).
[http://www.polychora.com/12GudapsMovie.gif Animation of cross sections]
Ditetragoltriates
Also related are the ditetragoltriates or octagoltriates, formed by taking the
octagon
In geometry, an octagon (from the Greek ὀκτάγωνον ''oktágōnon'', "eight angles") is an eight-sided polygon or 8-gon.
A '' regular octagon'' has Schläfli symbol and can also be constructed as a quasiregular truncated square, t, whi ...
(considered to be a ditetragon or a truncated square) to a p-gon. The ''octagon'' of a p-gon can be clearly defined if one assumes that the octagon is the convex hull of two perpendicular
rectangle
In Euclidean plane geometry, a rectangle is a quadrilateral with four right angles. It can also be defined as: an equiangular quadrilateral, since equiangular means that all of its angles are equal (360°/4 = 90°); or a parallelogram containi ...
s; then the p-gonal ditetragoltriate is the convex hull of two p-p duoprisms (where the p-gons are similar but not congruent, having different sizes) in perpendicular orientations. The resulting polychoron is isogonal and has 2p p-gonal prisms and p
2 rectangular trapezoprisms (a
cube
In geometry, a cube is a three-dimensional solid object bounded by six square faces, facets or sides, with three meeting at each vertex. Viewed from a corner it is a hexagon and its net is usually depicted as a cross.
The cube is the only r ...
with ''D
2d'' symmetry) but cannot be made uniform. The vertex figure is a
triangular bipyramid
In geometry, the triangular bipyramid (or dipyramid) is a type of hexahedron, being the first in the infinite set of face-transitive bipyramids. It is the dual of the triangular prism with 6 isosceles triangle faces.
As the name suggests, i ...
.
Double antiprismoids
Like the duoantiprisms as alternated duoprisms, there is a set of p-gonal double antiprismoids created by alternating the 2p-gonal ditetragoltriates, creating p-gonal antiprisms and tetrahedra while reinterpreting the non-corealmic triangular bipyramidal spaces as two tetrahedra. The resulting figure is generally not uniform except for two cases: the
grand antiprism and its conjugate, the pentagrammic double antiprismoid (with p = 5 and 5/3 respectively), represented as the alternation of a decagonal or decagrammic ditetragoltriate. The vertex figure is a variant of the
sphenocorona
In geometry, the sphenocorona is one of the Johnson solids (). It is one of the elementary Johnson solids that do not arise from "cut and paste" manipulations of the Platonic and Archimedean solids.
Johnson uses the prefix ''spheno-'' to ref ...
.
k_22 polytopes
The
3-3 duoprism
In the geometry of 4 dimensions, the 3-3 duoprism or triangular duoprism is a 4-polytope, four-dimensional convex polytope. It can be constructed as the Cartesian product of two triangles and is the simplest of an infinite family of four-dimensiona ...
, -1
22, is first in a dimensional series of uniform polytopes, expressed by
Coxeter as k
22 series. The 3-3 duoprism is the vertex figure for the second, the
birectified 5-simplex
In five-dimensional geometry, a rectified 5-simplex is a convex uniform 5-polytope, being a Rectification (geometry), rectification of the regular 5-simplex.
There are three unique degrees of rectifications, including the zeroth, the 5-simplex its ...
. The fourth figure is a Euclidean honeycomb,
222, and the final is a paracompact hyperbolic honeycomb, 3
22, with Coxeter group
2,2,3">2,2,3 . Each progressive
uniform polytope
In geometry, a uniform polytope of dimension three or higher is a vertex-transitive polytope bounded by uniform facets. The uniform polytopes in two dimensions are the regular polygons (the definition is different in 2 dimensions to exclude vert ...
is constructed from the previous as its
vertex figure
In geometry, a vertex figure, broadly speaking, is the figure exposed when a corner of a polyhedron or polytope is sliced off.
Definitions
Take some corner or Vertex (geometry), vertex of a polyhedron. Mark a point somewhere along each connect ...
.
See also
*
Polytope and
4-polytope
In geometry, a 4-polytope (sometimes also called a polychoron, polycell, or polyhedroid) is a four-dimensional polytope. It is a connected and closed figure, composed of lower-dimensional polytopal elements: vertices, edges, faces (polygons), an ...
*
Convex regular 4-polytope
*
Duocylinder
*
Tesseract
Notes
References
*''Regular Polytopes'',
H. S. M. Coxeter
Harold Scott MacDonald "Donald" Coxeter, (9 February 1907 – 31 March 2003) was a British and later also Canadian geometer. He is regarded as one of the greatest geometers of the 20th century.
Biography
Coxeter was born in Kensington t ...
, Dover Publications, Inc., 1973, New York, p. 124.
*
Coxeter, ''The Beauty of Geometry: Twelve Essays'', Dover Publications, 1999, (Chapter 5: Regular Skew Polyhedra in three and four dimensions and their topological analogues)
** Coxeter, H. S. M. ''Regular Skew Polyhedra in Three and Four Dimensions.'' Proc. London Math. Soc. 43, 33-62, 1937.
*
John H. Conway
John Horton Conway (26 December 1937 – 11 April 2020) was an English people, English mathematician active in the theory of finite groups, knot theory, number theory, combinatorial game theory and coding theory. He also made contributions to ...
, Heidi Burgiel, Chaim Goodman-Strass, ''The Symmetries of Things'' 2008, {{ISBN, 978-1-56881-220-5 (Chapter 26)
*
N.W. Johnson: ''The Theory of Uniform Polytopes and Honeycombs'', Ph.D. Dissertation, University of Toronto, 1966
4-polytopes