This book has greatly profited from collaborations and discussions with W.
Bulla, F. Gesztesy, H. Holden, M. Krishna, and B. Simon. In addition, many
people generously devoted considerable time and effort to reading earlier versions
of the manuscript and making many corrections. In particular, I wish to thank D.
Damanik, H. Hanfimann, A. von der Heyden, R. Killip, T. S0rensen, S. Timischl,
K. Unterkofler, and H. Widom. Next, I am happy to express my gratitude to P.
Deift, J. Geronimo, and E. Lieb for helpful suggestions and advise. I also like to
thank the staff at the American Mathematical Society for the fast and professional
production of this book.
Partly supported by the Austrian Science Fund (http: //www. f wf . ac. a t / ) un-
der Grant No. P12864-MAT.
Finally, no book is free of errors. So if you find one. or if you have comments
or suggestions, please let me know. I will make all corrections and complements
available at the URL above.
Institut fur Mathematik
1090 Wien, Austria
E-mail address: gerald@mat. univie . ac . at
URL: http://www.mat .univie.ac.at/~gerald /