This is a reissue of Professor Coxeter's classic text on non-Euclidean geometry. It begins with a historical introductory chapter, and then devotes three chapters to surveying real projective geometry ...

This book gives a rigorous treatment of the fundamentals of plane geometry: Euclidean, spherical, elliptical and hyperbolic. The primary purpose is to acquaint the reader with the classical results of ...

Keep in mind, however, that the above rule (namely, that the angles of a triangle add up to 180 degrees) is not false. In fact, it is true - however, it is only true in Euclidean geometry.

A flat geometry is a Euclidean geometry, named after the ancient Greek mathematician Euclid, wherein parallel lines remain parallel and the angles of a triangle add up to 180 degrees. So which is it?