A book is never the sole accomplishment of the authors. It is built on the foun- dation of established mathematics, and it benefits from current developments within the mathematical community. Many colleagues have contributed ideas, comments, and corrections to this volume. There are, first of all, our students C. Bauer, G. Grammel, 1. Greger, S. Grtinvogel, G. Hackl, and D. Szolnoki in Augs- burg, and E. Joseph, R.-G. Lai, S. Lin, C.-M. Ou, and H. Wang in Ames. We have received comments from, among others, L. Arnold, V. Ayala, K. Grasse, D. Hinrichsen, R. Johnson, Y. Latushkin, J.L. Massera,...