Case number 27

Boy's surface with symmetry axis Boy's surface with symmetry axis Desargues' theorem in space and in the plane
10 pairwise orthogonal lines Tetrahedron in the projective space Projective plane
Two regular each other penetrating tetrahedrons Heptahedron (one-sided surface) Two regular each other penetrating tetrahedrons

The corresponding bottom case is: Case number U 27

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