| Monogon | |
| Type: | Regular polygon |
| Edges: | 1 |
| Schläfli: | or h |
| Coxeter: | or |
| Symmetry: | [], Cs |
| Dual: | Self-dual |
In geometry, a monogon, also known as a henagon, is a polygon with one edge and one vertex. It has Schläfli symbol .[1]
In Euclidean geometry a monogon is a degenerate polygon because its endpoints must coincide, unlike any Euclidean line segment. Most definitions of a polygon in Euclidean geometry do not admit the monogon.
In spherical geometry, a monogon can be constructed as a vertex on a great circle (equator). This forms a dihedron,, with two hemispherical monogonal faces which share one 360° edge and one vertex. Its dual, a hosohedron, has two antipodal vertices at the poles, one 360° lune face, and one edge (meridian) between the two vertices.