1. Bishop, R., O'Neill, B., Manifolds of negative curvature, Trans. Amer. Math. Soc. 145 (1969), 1–49.
2. Bogomolov, F.A., Holomorphic tensors and vector bundles on projective varities, Izv. Akad. nauk SSSR, Ser. Mat. 42 (1978), no. 6, 1227–1287 (English transl.: math. USSR, Izv, 13 (1979), 499–555).
3. Bridson, M., Haefliger, A., Metric spaces of non-positive curvature, Springer (1999).
4. Cartan, E., Groupes simples clos et ouverts et géométrie Riemannienne, J. Math. Pures Appl. 8 (1929), 1–33.
5. Helgason, S., Differential Geometry, Lie groups and symmetric spaces, Academic Press (1978).