1. V. N. Berestovskiî, “Homogeneous manifolds with intrinsic metric. II,” Sibirsk. Mat. Zh.,30, No. 2, 14–28 (1989).
2. S. Sasaki, “On the differential geometry of tangent bundles of Riemannian manifolds,” Tôhoku Math. J. (2),10, 338–3540 (1958); II:14, 146–155 (1962).
3. R. S. Strichartz, “Sub-Riemannian geometry,” J. Differential Geom.,24, 221–263 (1986).
4. A. D. Alexandrov, “Über eine Verallgemeinerung der Riemannschen Geometrie,” Schrift. Inst. Math. der Deutschen Acad. Wiss., No. 1, 33–84 (1957).
5. V. N. Berestovskiî, “Submetries of space forms of nonnegative curvature,” Sibirsk. Mat. Zh.,28, No. 4, 44–56 (1987).