1. Intrinsic Geometry of Surfaces;Alexandrov,1967
2. A.D. Alexandrov Selected Works. Part II. Intrinsic Geometry of Convex Surfaces;Alexsandrov,2006
3. Metric Spaces of Non-positive Curvature;Bridson,1999
4. The Geometry of Geodesics;Busemann,1955
5. An Introduction to Riemann-Finsler Geometry;Dai-Wai Bao,2000