Hemi-icosahedron

It can be realized as a projective polyhedron (a tessellation of the real projective plane by 10 triangles), which can be visualized by constructing the projective plane as a hemisphere where opposite points along the boundary are connected and dividing the hemisphere into three equal parts.

It is also related to the nonconvex uniform polyhedron, the tetrahemihexahedron, which could be topologically identical to the hemi-icosahedron if each of the 3 square faces were divided into two triangles.

It can be represented symmetrically on faces, and vertices as Schlegel diagrams: It has the same vertices and edges as the 5-dimensional 5-simplex which has a complete graph of edges, but only contains half of the (20) faces.

From the point of view of graph theory this is an embedding of

(the complete graph with 6 vertices) on a real projective plane.

The complete graph K 6 represents the 6 vertices and 15 edges of the hemi-icosahedron