Authors
Dimitrios Georgiou
Department of Mathematics, University of Patras, Patra, Greece
Yasunao Hattori
Shimane University (Professor Emeritus), JAPAN; National Institution for Academic Degrees and Quality Enhancemnent of Higher Education, Kodaira, Japan
Athanasios Megaritis
Department of Mathematics, University of Patras, Patra, Greece
Fotini Sereti
Department of Mathematics, University of Western Macedonia, Kastoria, Greece