1. T. Jørgensen, “A note on subgroups of SL(2, C),” Quart. J. Math. Oxford Ser. (2) 28 (110), 209–211 (1977).
2. A. F. Beardon, The Geometry of Discrete Groups (Academic Press, London, 1977; Nauka, Moscow, 1986).
3. T. Jørgensen, “On discrete groups of Möbius transformations,” Amer. J. Math. 98 (3), 739–749 (1976).
4. A. Yu. Vesnin and A. V. Maslei, Two-Generated Subgroups of PSL(2, C) Extremal for the Jørgensen Inequality and Its Analogs, in Proceedings of the Seminar on Vector and Tensor Analysis and Its Applications to Geometry, Mechanics, and Physics (Izd. Moskov. Univ., Moscow, 2014), Vol. 30 [in Russian].
5. T. Jørgensen and M. Kiikka, “Some extreme discrete groups,” Ann. Acad. Sci. Fenn. Ser. A I, Math. 1 (2), 245–248 (1975).