International
Tables for Crystallography Volume A Spacegroup symmetry Edited by M. I. Aroyo © International Union of Crystallography 2016 
International Tables for Crystallography (2016). Vol. A, ch. 2.1, p. 157


Figure 2.1.3.9
Rhombohedral space groups. Obverse triple hexagonal cell with `hexagonal axes' a, b and primitive rhombohedral cell with projections of `rhombohedral axes' a_{rh}, b_{rh}, c_{rh}. Note: In the actual spacegroup diagrams the edges of the primitive rhombohedral cell (dashed lines) are only indicated in the generalposition diagram of the rhombohedralaxes description ( = generalposition diagram). 