Digon

A digon is a polygon with two sides. It is degenerate if embedded in Euclidean space, as its edges coincide. It can however be thought of as a tiling of the circle. In two-dimensional or higher spherical space, it can form a lune such as the ones making up a hosohedron.

In Euclidean space, a convex n-gon can be formed as the intersection of n half-planes, so one possible realization of a Euclidean digon is as the intersection of two parallel half-planes, forming an infinite "stripe."

It is the only two-dimensional ditope and hosotope. It is also the two-dimensional demihypercube.

The digon is the only non-lattice polygon and the simplest non-lattice polytope. In turn, many (though not all) non-lattice polytopes contain digonal sections.

The digon is the simplest possible polygon, as monogons are disallowed under almost all definitions of a polytope. Despite this, it may be built as the omnitruncate of a (generalized) complex with two flags and two flag-changes between them. As such, this complex is called the monogonal complex.