1. I.M.B., UMR 5584 du CNRS, B.P. 47 870, 21078 Dijon Cedex, France
2. Department of Mathematics of Nizhnii Novgorod SA Academy, 97 Gagarin av. Nizhnii Novgorod, 603107, Russia
3. Department of function theory Nizhnii Novgorod State University, 23 Gagarin av. Nizhnii Novgorod, 603950, Russia