Digon

Regular digon
On a circle, a digon is a tessellation with two antipodal points, and two 180° arc edges.
Type	Regular polygon
Edges and vertices	2
Schläfli symbol	{2}
Coxeter–Dynkin diagrams
Symmetry group	D2, [2], (*2•)
Internal angle (degrees)	0° (convex)
Dual polygon	Self-dual

In geometry, a bigon,^[1] digon, or a 2-gon, is a polygon with two sides (edges) and two vertices. Its construction is degenerate in a Euclidean plane because either the two sides would coincide or one or both would have to be curved; however, it can be easily visualised in elliptic space. It may also be viewed as a representation of a graph with two vertices, see "Generalized polygon".

A regular digon has both angles equal and both sides equal and is represented by Schläfli symbol {2}. It may be constructed on a sphere as a pair of 180 degree arcs connecting antipodal points, when it forms a lune.

The digon is the simplest abstract polytope of rank 2.

A truncated digon, t{2} is a square, {4}. An alternated digon, h{2} is a monogon, {1}.