horsecez@gmail.com
daniel_klich@sggw.pl
nyasynetska@gmail.com
martazygowska@gmail.com
© 2020 K. Slivinska, D. Klich, N. Yasynetska, M. Żygowska, published by Slovak Academy of Sciences, Mathematical InstituteThis work is licensed under the Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 License.