1. S. A. Akbarov and V. A. Toponogov, ?Comparison theorem for angles of a triangle for a class of Riemannian manifolds,? Tr. Inst. Mat. Sib. Otd. Akad. Nauk SSSR,9, 16?25 (1987).
2. R. Bishop and R. D. Crittenden, Geometry of Manifolds [Russian translation], Mir, Moscow (1967).
3. A. A. Borisenko and A. L. Yampol'skii, ?Sasaki metric of the normal bundle of a submanifold of a Riemannian space,? Mat. Sb.,134, No. 2, 158?176 (1987).
4. Yu. D. Burago, ?Three-dimensional open Riemannian spaces of nonnegative curvature,? Zap. Nauchn. Semin. Leningr. Otd. Mat. Inst.,66, 103?113 (1976).
5. Yu. D. Burago, ?Homotopy type of Riemannian manifolds with boundary under restrictions on their p-dimensional curvatures and the p-mean curvature of the boundary,? in: Ninth National Geometry Conference. Kishinev, Sept., 1988. Abstracts of Reports [in Russian], Kishinev (1988), pp. 54?55.