Given a point and a Line , draw the Perpendicular through and call it . Let be any other
line from which meets in . In a Hyperbolic Geometry, as moves off to infinity along , then the
line approaches the limiting line , which is said to be parallel to at . The angle which
makes with is then called the Angle of Parallelism for perpendicular distance , and is given by
See also Angle of Parallelism, Hyperbolic Geometry
Manning, H. P. Introductory Non-Euclidean Geometry. New York: Dover, p. 58, 1963.