Institution: | 1. Laboratory of Mathematics of the University of Saint-Etienne (LAMUSE) EA 3989, University of Lyon , 23 rue P.Michelon, 42023, Saint-Etienne , France grigory.panasenko@univ-st-etienne.fr;3. Department of Mathematics and Informatics , Vilnius University , Naugarduko Str., 24, LT–03225 Vilnius , Lithuania |