This volume comprises lecture notes, survey and research articles originating from the CIMPA Summer School Arithmetic and Geometry around Hypergeometric Functions held at Galatasaray University, Istanbul, June 13-25, 2005. It covers a wide range of topics related to hypergeometric functions, thus giving a broad perspective of the state of the art in the field.

Bei hoherdimensionalen komplexen Mannigfaltigkeiten stellt die Riemann-Roch-Theorie die grundlegende Verbindung von analytischen bzw. algebraischen zu topologischen Eigenschaften her. Dieses Buch befasst sich mit Mannigfaltigkeiten der komplexen Dimension 2, d. h. mit komplexen Flachen. Hauptziel der Monographie ist es, neue rationale diskrete Invarianten (Hohen) in die Theorie komplexer Flachen explizit einzufuhren und ihre Anwendbarkeit auf konkrete aktuelle Probleme darzustellen.Als erste unmittelbare Anwendung erhalt man explizit und ganz allgemein Formeln vom Hurwitz-Typ endlicher Flachenuberlagerungen fur die vier klassischen Invarianten, die auf andere Weise bisher nur in Spezialfallen zuganglich waren. Ein weiteres Anwendungsgebiet ist die Theorie der Picardschen Modulflachen: Neue Resultate werden beschrieben. Letztendlich kann im letzten Kapitel eine Erganzung des bekannten Satzes von Bogomolov-Miyaoka-Yau mit Hilfe der Hohentheorie gezeigt werden.
The monograph presents basically an arithmetic theory of orbital surfaces with cusp singularities. As main invariants orbital hights are introduced, not only for the surfaces but also for the components of orbital cycles. These invariants are rational numbers with nice functorial properties allowing precise formulas of Hurwitz type and a fine intersection theory for orbital cycles. For ball quotient surfaces they appear as volumes of fundamental domains. In the special case of Picard
modular surfaces they are discovered by special value of Dirichlet L-series or higher Bernoulli numbers. As a central point of the monograph a general Proportionality Theorem in terms of orbital hights is proved. It yields a strong criterion to decide effectively whether a surface with given cycle supports a ball quotient structure being Kaehler-Einstein with negative constant holomorphic sectional curvature outside of this cycle. The theory is applied to the classification of Picard modular surfaces and to surfaces geography."

As an interesting object of arithmetic, algebraic and analytic geometry the complex ball was born in a paper of the French Mathematician E. PICARD in 1883. In recent developments the ball finds great interest again in the framework of SHIMURA varieties but also in the theory of diophantine equations (asymptotic FERMAT Problem, see ch. VI). At first glance the original ideas and the advanced theories seem to be rather disconnected. With these lectures I try to build a bridge from the analytic origins to the actual research on effective problems of arithmetic algebraic geometry. The best motivation is HILBERT'S far-reaching program consisting of 23 prob lems (Paris 1900) " . . . one should succeed in finding and discussing those functions which play the part for any algebraic number field corresponding to that of the exponential function in the field of rational numbers and of the elliptic modular functions in the imaginary quadratic number field." This message can be found in the 12-th problem "Extension of KRONECKER'S Theorem on Abelian Fields to Any Algebraic Realm of Rationality" standing in the middle of HILBERTS'S pro gram. It is dedicated to the construction of number fields by means of special value of transcendental functions of several variables. The close connection with three other HILBERT problems will be explained together with corresponding advanced theories, which are necessary to find special effective solutions, namely: 7. Irrationality and Transcendence of Certain Numbers; 21."