Download the full article as a PDF file.
© 2018 Viktoria Volodina, Natalia Karygina, Olga Popova, Elmira Popova, Mariia Grushko, Nadezhda Fedorova, published by Slovak Academy of Sciences, Mathematical Institute
This work is licensed under the Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 License.