Affiliation: | (1) Institute of Mathematics and Computer Science, Wrocław University of Technology, Wybrzeże Wyspiańskiego 27, 50-370 Wrocław, Poland;(2) Department of Mathematics, Hubei Institute for Nationalities, 445000 Enshi, Hubei Province, People’s Republic of China;(3) Department of Mathematics, Yazd University, Yazd, Iran |