1. Department of Mathematics National Technical University, Zografou Campus Athens Greece
2. Department of Mathematics University of Craiova Craiova Romania
3. Faculty of Applied Mathematics AGH University of Kraków Kraków Poland
4. Simion Stoilow Institute of Mathematics of the Romanian Academy Bucharest Romania
5. Brno University of Technology, Faculty of Electrical Engineering and Communication Brno Czech Republic
6. Department of Mathematics Zhejiang Normal University Jinhua Zhejiang China
7. School of Mathematics and Statistics HNP‐LAMA, Central South University Changsha Hunan P.R. China