*George E. Martin, "The Foundations of Geometry and the Non-Euclidean Plane", Springer-Verlag, 1975*M. J. Greenberg, "Euclidean and Non-Euclidean Geometries: Development and History", 4th edition, W. H. Freeman, 2008.
== Examples ==== See also ==* Non-Euclidean geometry==Notes====References==*George E. Martin, "The Foundations of Geometry and the Non-Euclidean Plane", Springer-Verlag, 1975*M. J. Greenberg, "Euclidean and Non-Euclidean Geometries: Development and History", 4th edition, W. H. Freeman, 2008.