Stellated square

The compound of two digons, also called the stellated square, is a regular polygon compound, being the compound of two digons. As such it has 4 edges and 4 vertices. It is degenerate if embedded in Euclidean space, as its edges coincide. However it has a non-degenerate embeddeding on the surface of a 2-sphere.

It can be formed as a degenerate stellation of the square, by extending the edges to infinity.

Its quotient prismatic equivalent is the tetrahedron, which is three-dimensional.

Vertex coordinates
Coordinates for the vertices of a compound of two digons of edge length 1 centered at the origin are given by:
 * $$\left(±\frac{\sqrt2}{2},\,±\frac{\sqrt2}{2}\right).$$