Affiliation: | (1) Department of Mathematics, University of Napoli, Via Monteoliveto 3, 80134 Napoli, Italy;(2) Institute of Cybernetics Academy of Sciences of Georgia, S. Euli Str. 5, Tbilisi, 380086, Georgia;(3) Department of Mathematics, niversity of Udine, Via delle Scienze 208, 33100 Udine, Italy |