International
Tables for Crystallography Volume A Spacegroup symmetry Edited by Th. Hahn © International Union of Crystallography 2006 
International Tables for Crystallography (2006). Vol. A, ch. 4.1, p. 56

The synoptic tables of this section comprise two features:
For each crystal system, the text starts with a historical note on the synoptic tables in the earlier editions of International Tables^{1} followed by a discussion of points (i) and (ii) above. Finally, those group–subgroup relations (cf. Section 8.3.3 ) are treated that can be recognized from the full and the extended Hermann–Mauguin spacegroup symbols. This applies mainly to the translationengleiche or t subgroups (type I, cf. Section 2.2.15 ) and to the klassengleiche or k subgroups of type IIa. For the k subgroups of types IIb and IIc, inspection of the synoptic Table 4.3.2.1 provides easy recognition of only those subgroups which originate from the decentring of certain multiple cells: C or F in the tetragonal system (Section 4.3.4 ), R and H in the trigonal and hexagonal systems (Section 4.3.5 ).
References
International Tables for Xray Crystallography (1952). Vol. I, edited by N. F. M. Henry & K. Lonsdale. Birmingham: Kynoch Press. [Abbreviated as IT (1952).]