Space group symbol defined by Hall (Acta Cryst. (1981) A37,
517-525) (See also International Tables for Crystallography
Vol.B (1993) 1.4 Appendix B).
Each component of the space group name is separated by a
space or an underscore. The use of space is strongly
recommended. The underscore is only retained because it
was used in earlier archived files. It should not be
used in new CIFs.
_space_group.name_Hall uniquely defines the space group and
its reference to a particular coordinate system.