Figs. 1238.26A. B, C: In this plane net of four hinged triangles the dotted line indicates the intersection of a great-circle plane passing through the assembled tetra. Four edge-bonded triangles of the tetra with great-circle plane passing through. The same four triangles may be vertex-bonded to describe an octahedron with alternate open and closed faces. (via Fig. 1238.26)
