Dihedron

Set of regular n-gonal dihedra
Example hexagonal dihedron on a sphere
Type	regular polyhedron or spherical tiling
Faces	2 n-gons
Edges	n
Vertices	n
Vertex configuration	n.n
Wythoff symbol	2 | n 2
Schläfli symbol	{n,2}
Coxeter diagram
Symmetry group	Dnh, [2,n], (*22n), order 4n
Rotation group	Dn, [2,n]+, (22n), order 2n
Dual polyhedron	regular n-gonal hosohedron

A dihedron is a type of polyhedron, made of two polygon faces which share the same set of n edges. In three-dimensional Euclidean space, it is degenerate if its faces are flat, while in three-dimensional spherical space, a dihedron with flat faces can be thought of as a lens, an example of which is the fundamental domain of a lens space L(p,q).^[1] Dihedra have also been called bihedra,^[2] flat polyhedra,^[3] or doubly covered polygons.^[3]

As a spherical tiling, a dihedron can exist as nondegenerate form, with two n-sided faces covering the sphere, each face being a hemisphere, and vertices on a great circle. It is regular if the vertices are equally spaced.

The dual of an n-gonal dihedron is an n-gonal hosohedron, where n digon faces share two vertices.