1. see, e.g., G. G. Koerber. Properties of Solids, Prentice-Hall, Englewood Cliffs, 1962; A. H. Cottrell, The Mechanical Properties of Matter, Wiley and Sons, New York, 1964; J. F. Nye, Physical Properties of Crystals, Clarendon Press, Oxford, 1957; F. C. Phillips, An Introduction to Crystallography, Wiley, New York, 1963.
2. The list often includes a rotational axis in combination with a point of inversion on the axis.
3. Lekhnitskii, op. cit.
4. As noted by Eringen, the existence of two orthogonal planes of material symmetry implies automatically the symmetry with respect to the third orthogonal plane. See Eringen, (1967). op. cit., p. 191.
5. Lekhnitskii, op. cit., p. 19, after a suitable change of notation of coordinate axes, and correction of the order of suffixes in Poisson’s coefficients.