Hermann-Mauguin space-group symbol. Note that the
Hermann-Mauguin symbol does not necessarily contain complete
information about the symmetry and the space-group origin. If
used, always supply the FULL symbol from International Tables
for Crystallography Vol. A (2002) and indicate the origin and
the setting if it is not implicit. If there is any doubt that
the equivalent positions can be uniquely deduced from this
symbol, specify the _symmetry_equiv.pos_as_xyz or
_symmetry.space_group_name_Hall data items as well. Leave
spaces between symbols referring to
different axes.