Assertion: octahedron's face | /r/CapableOf | form regular pattern of triangles
Facets:
Source sentences:
text: Because the faces on the planes separating these layers form a regular pattern of triangles, adjacent layers can be placed so that each octahedron in one layer meets a tetrahedron in the next layer, or so that each cell meets a cell of its own kind (the layer boundary thus becomes a reflection plane).