Assertion: octahedron's vertex | /r/HasProperty | grouped into two groups of four
Facets:
Source sentences:
text: The vertices of a cube can be grouped into two groups of four, each forming a regular tetrahedron (see above, and also animation, showing one of the two tetrahedra in the cube).
text: The vertices of a cube can be grouped into two groups of four, each forming a regular tetrahedron; more generally this is referred to as a demicube.