Contains all the data items that refer to the space group as a
               whole, such as its name, Laue group etc.  It may be looped, for
               example, in a list of space groups and their properties.

               Space group types are identified by their International Tables
               for Crystallography Vol A number or Schoenflies symbol.  
               Specific settings of the space groups can be identified by
               their Hall symbol, by specifying their symmetry operations or
               generators, or by giving the transformation that relates the
               specific setting to the reference setting based on
               International Tables for Crystallography Vol. A and stored in
               this dictionary.

               The commonly-used Hermann-Mauguin symbol determines the
               space group type uniquely but several different Hermann-Mauguin
               symbols may refer to the same space group type. It contains
               information on the choice of the basis, but not on the
               choice of origin.