In two dimensions, the rectangular group [2], abstract D 2 or D 4, also can be represented as a direct product [ ]×[ ], being the product of two bilateral groups, represents two orthogonal mirrors, with Coxeter diagram, , with order 4. The 2 in [2] comes from linearization of the orthogonal subgraphs in the Coxeter diagram, as with explicit branch order 2. The rhombic group, [2] ( or ), half of the rectangular group, the point reflection symmetry, Z 2, order 2.