Figure 6
The two possible tetrahedron layers that can be stacked on a given layer, always one with the same relative orientation and the other rotated by 180°: (a) T2 or T3′ on T1, (b) T3 or T1′ on T2, (c) T1 or T2′ on T3, (d) T2 or T3′ on T1′, (e) T3 or T1′ on T2′, and (f) T1 or T2′ on T3′. |