1. International Tables for Crystallography. Vol. A. Space-Group Symmetry, Ed. by T. Hahn (Reidel, Dordrecht, Holland, 1983), p. 869.
2. E. Koch and V. Fischer, Acta Cryst., Sect. A: Cryst. Phys., Diffr., Theor. Gen. Crystallogr. 31, 88 (1975).
3. V. I. Burdina, Dokl. Akad. Nauk 350, 78 (1996) [Phys. Dokl. (1996)].
4. V. I. Burdina, Dokl. Akad. Nauk 328, 459 (1993) [Phys. Dokl. 38, 49 (1993)].
5. A. G. Kurosh, The Theory of Groups (Nauka, Moscow, 1967, 3rd ed.; Chelsea, New York, 1960, 2nd ed.).