1. Beardon A.F.: The geometry of discrete groups. Grad. Texts Math., vol. 91. Springer, Berlin (1983)
2. Beresnevich, V., Velani, S.: Ubiquity and a general logarithm law for geodesics. In: Drutu, C., Dal’Bo, F., Bugeaud, Y. (eds.) Dynamical systems and Diophantine approximation (Institut Henri Poincaré, 7–9 June 2004), Séminaires et Congrès, vol. 20, Soc. Math. France; see also [arXiv:0707.1225] (to appear)
3. Bianchi L.: Sui gruppi di sostituzioni lineari con coefficienti appartenenti a corpi quadratici immaginari. Math. Ann. 40, 332–412 (1892)
4. Borel A.: Linear algebraic groups. In: Borel, A., Mostow, G.D. (eds) Algebraic Groups and Discontinuous Subgroups (Proc. Sympos. Pure Math., Boulder, 1965), pp. 3–19. American Mathematical Society, Providence (1996)
5. Borel A.: Harish-Chandra: Arithmetic subgroups of algebraic groups. Ann. Math. 75, 485–535 (1962)