قطع الشوارع رياضيًّا

1-  Venema, Gerard A. (2006), Foundations of Geometry, Prentice-Hall, p. 8 [Book], Available from: هنا
2- Lee, John M. (1991), Riemannian Manifolds - An Introduction to Curvature p. 164 [Book] 
3- Sommerville, D.M.Y. (2005). The elements of non-Euclidean geometry, p. 58 [Book]