1. Institute for Information Transmission Problems, Bolshoi Karetnyi per., 19, 127051 Moscow, Russia
2. Masaryk University, Kotlarska 2, 61137 Brno, Czech Republic
3. Department of Mathematics and Center for Mathematical Physics, University of Hamburg, Bundesstraße 55, D-20146 Hamburg, Germany
4. Department of Mathematics, Faculty of Education, Niigata University, 8050 Ikarashi-Nino-cho, Nishi-ku, 950-2181 Niigata, Japan
5. Department of Mathematics, Josai University, Keyaki-dai 1-1, Sakado, 350-0295 Saitama, Japan