| Affiliation: | 1. Department of Mathematics, Faculty of Engineering, Graduate School of Environment and Information Sciences, Yokohama National University, 156 Tokiwadai, Hodogayaku, Yokohama 240, Japan;2. Faculty of Mathematics and Computer Science, Nicolaus Copernicus University, PL-87-100 Toruń, ul. Chopina 12/18, Poland;1. Dipartimento di Matematica e Fisica, Università degli Studi di Roma Tre, L.go S. Leonardo Murialdo 1, 00146 Roma, Italy;2. Dipartimento di Matematica, Università di Roma “La Sapienza”, P.le Aldo Moro 5, 00185 Roma, Italy;1. University of Roma ‘Sapienza’, P.le Aldo Moro 5, 00185 Roma, Italy;2. University of Campania ‘Luigi Vanvitelli’, V.le Lincoln 5, 81100 Caserta, Italy |
