\begin{thebibliography}{BBNWZ78} \bibitem[BBNWZ78]{BBNWZ78} H. Brown, R. B{\accent127 u}low, J. Neub{\accent127 u}ser, H. Wondratschek, and H. Zassenhaus. \newblock {\em Crystallographic Groups of Four-Dimensional Space}. \newblock John Wiley, New York, 1978. \bibitem[Hah95]{Hah95} T. Hahn, editor. \newblock {\em International Tables for Crystallography, Volume A, Space-group Symmetry, 4th Edition}. \newblock Kluwer, Dordrecht, 1995. \bibitem[NPW81]{NPW81} J. Neub{\accent127 u}ser, W. Plesken, and H. Wondratschek. \newblock An emendatory discursion on defining crystal systems. \newblock {\em Match}, 10:77--96, 1981. \end{thebibliography}