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  Modern Geometries: Non-Euclidean, Projective, and Discrete - Michael Henle - Google Books

  http://books.google.de/books?id=84IpAQAAMAAJ

  Engaging, accessible, and extensively illustrated, this brief, but solid introduction to modern geometry describes geometry as it is understood and used by contemporary mathematicians and theoretical scientists. Basically non-Euclidean in approach, it…

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  Discontinuous Groups of Isometries in the Hyperbolic Plane - Werner Fenchel, Jakob Nielsen - Google Books

  http://books.google.de/books?id=IJC3ojxMamEC

  This is an introductory textbook on isometry groups of the hyperbolic plane. Interest in such groups dates back more than 120 years. Examples appear in number theory (modular groups and triangle groups), the theory of elliptic functions, and the theory of…

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