1. Department of Mathematics, National Technical University of Athens, 15780, Athens, Greece.
2. Department of Information Engineering, Computer Science, and Mathematics, University of L’Aquila, 67100, L’Aquila, Italy.
3. L2S-CentraleSupélec and Université Paris-Saclay, Institut Universitaire de France, Gif-sur-Yvette, France.
4. Department of Mathematical Sciences, Florida Atlantic University, Boca Raton, FL 33431 USA.