1. Department of Mathematics, Darmstadt University of Technology, 64283 Darmstadt, Germany. E-mail: farwig@mathematik.tu-darmstadt.de
2. Mathematics Department, University of Erlangen-Nuremberg, 91058 Erlangen, Germany. E-mail: raphael.schulz@math.fau.de
3. Department of Mathematics, Faculty of Science and Engineering, Waseda University, Tokyo, Japan. E-mail: masao.yamazaki@waseda.jp