1. Department of Mathematics, State University of New York at Buffalo, Buffalo, New York 14260, USA
2. Department of Physics, State University of New York at Buffalo, Buffalo, New York 14260, USA
3. Department of Science Education and Mathematics, Mid Sweden University, S-851 70 Sundsvall, Sweden
4. Instytut Matematyki, Uniwersytet Jana Kochanowskiego w Kielcach, Poland