1. Bouckaert, L.P., Smoluchowski, R. and Wigner, E. (1936). Phys. Rev., 50, 58.
2. Bradley, C.J. and Cracknell, A.P. (1972). The Mathematical Theory of Symmetry in Solids: Representation Theory for Point Groups and Space Groups, (Clarendon Press, Oxford).
3. Cowley, R.A. (1964). Phys. Rev., 134, A981.
4. Johnson, F.A. and Loudon, R. (1964). Proc. Roy. Soc., A281, 274.
5. Poulet, H. (1965). J. Phys. (Paris), 26, 684.