References
- Trans. Amer. Math. Soc. v.145 Manifolds of negative curvature R.L.Bishop;B.O'Neill
- Geometry of submanifolds B.Y. Chen
- Proc. Japan Acad v.71 Warped products with critical Riemannian metric B.H. Kim
- Semi-Riemannian geometry with application to relativity B. O'Neill