1. Topological dynamics on nilmanifolds;Auslander, L.;Bull. Amer. Math. Soc.,1961
2. Fuchsian groups and transitive horocycles;Hedlund, Gustav A.;Duke Math. J.,1936
3. 3. E. Hopf, Statistik der geodätischen Linien in Mannigfaltigkeiten negativer Krümmung, Ber. Verh. Sächs. Akad. Wiss. Leipzig. Math.-Nat. Kl. vol. 51 (1939) pp. 261-304.
4. Geodesic flows on manifolds of constant negative curvature;Gel′fand, I. M.;Amer. Math. Soc. Transl. (2),1955
5. Spectra of nilflows;Green, L. W.;Bull. Amer. Math. Soc.,1961