1. Department of Mathematics, National Technical University, Zografou Campus, 15780 Athens, Greece
2. Department of Mathematics and Computer Science, University of Palermo, Via Archirafi 34, 90123 Palermo, Italy
3. Nonlinear Analysis Research Group, Ton Duc Thang University, Ho Chi Minh City, Vietnam and Faculty of Mathematics and Statistics, Ton Duc Thang University, Ho Chi Minh City, Vietnam