Császár polyhedron

The Csaszar polyhedron is a non-convex polyhedron with a hole consisting of 14 triangular sides, 21 edges and 7 vertices. It has no diagonals, and is next to the tetrahedron, the only known polyhedra with this property ( with the additional condition relating to the edge of a manifold). Each pair of vertices is connected by an edge.

The polyhedron has the topology of a torus ( Euler characteristic )

It was introduced in 1949 by Akos Csaszar.

It is dual to the Szilassi polyhedra.