1. University of Piteşti, Str. Târgu din Vale, nr. 1, 110040 Piteşti, Romania. armandmihai.ionescu@gmail.com
2. Institute of Mathematics of the Romanian Academy, PO Box 1-764, 014700 Bucharest, Romania. gpaun@us.es
3. Research Group on Natural Computing, Department of Computer Science and AI, University of Sevilla, Avda Reina Mercedes s/n, 41012 Sevilla, Spain. marper@us.es
4. Department of Mathematics, School of Education, Waseda University, 1-6-1 Nishi-waseda, Shinjuku-ku, Tokyo 169-8050, Japan. yokomori@waseda.jp