This book was accepted in 1999 as doctoral thesis (Dr. oec. publ. ) by the faculty of economics of the Ludwig-Maximilians-Universitat in Munich. It won the dissertation price of the Alumni-Club of the economics faculty in the academic year 2000. Financial assistance by the German Research Asso ciation (DFG) for printing costs is gratefully acknowledged. I have to thank the people behind the B'IF, X-project, in particular Donald Knuth and Leslie Lamport, for their wonderful typesetting program. The supervisors of my thesis were Prof. Dr. G. Flaig and Prof. Dr. D. Marin. I would like thank both...