## New material in the second online edition of Volume A

There are eight new chapters in this edition of Volume A and five chapters have been revised.

All the chapters in Part 1 (Introduction to space-group symmetry) are new. The first six of these form a homogeneous introductory text suitable for advanced undergraduate and postgraduate students of crystallography, and for researchers
from other fields. Chapter 1.7 gives an overview of the kinds of data to be found in the related Volumes A1 (*Symmetry relations between space groups*) and E (*Subperiodic groups*). In Part 3 there is a new chapter on magnetic subperiodic groups and magnetic space groups.

A further five chapters have been updated: Chapter 2.1 (Guide to the use of the space-group tables), Chapter 3.1 (Crystal lattices), Chapter 3.2 (Point groups and crystal classes), Chapter 3.4 (Lattice complexes) and Chapter 3.5 (Normalizers of space groups and their use in crystallography).

The layout of the space-group tables has been simplified as the sub- and supergroup data are now available in Volume A1. To simplify the use of the symmetry-element diagrams for the three different projections of the orthorhombic space groups, the corresponding origins and basis vectors are explicitly labelled (as in the diagrams of the monoclinic space groups). Modifications to the tabulated data and diagrams of the seven trigonal space groups of the rhombohedral lattice system include (i) changes in the sequence of coordinate triplets of some special Wyckoff positions of five rhombohedral groups in the rhombohedral-axes settings in order to achieve correspondence between the sequences of coordinate triplets of the rhombohedral and hexagonal descriptions, and (ii) labelling of the basis vectors (cell edges) of the primitive rhombohedral cell in the general-position diagrams of the rhombohedral-axes setting descriptions of all rhombohedral space groups. There are new general-position diagrams for the cubic space groups. Additional diagrams showing tilted, perspective views of some of the more complex cubic space groups are also provided in the print edition; these are provided for all of the cubic space groups in the online edition.

Further information about all these changes can be found in the Preface.

All known errors in the first edition have also been corrected.