Hemi-icosahedron

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Hemi-icosahedron
Hemi-icosahedron
Type abstract regular polyhedron
Faces 10 triangles
Edges 15
Vertices 6
Vertex configuration 3.3.3.3.3
Symmetry group A5
Dual hemi-dodecahedron
Properties non-orientable

A hemi-icosahedron is an abstract regular polyhedron, containing half the faces of a regular icosahedron. It exists on a hemisphere as a projective plane where opposite points along the boundary are connected.

It has 10 triangular faces, 15 edges, and 6 vertices. It has the same vertices and edges as the 5-dimensional polytope, the 5-simplex, but only contains half of the (20) faces.

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.

The complete graph K6 represents the 6 vertices and 15 edges of the hemi-icosahedron
The complete graph K6 represents the 6 vertices and 15 edges of the hemi-icosahedron

From the point of view of graph theory this is an embedding of K6 (the complete graph with 6 vertices) on a projective plane. With this embedding, the dual graph is the Petersen graph --- see hemi-dodecahedron.

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