Authors
Leonid Vasilyev
Department of Mathematics, University of Bergen, Postboks,, Bergen, Norway
Florin Adrian Radu
Department of Mathematics, University of Bergen, Postboks,, Bergen, Norway
© 2018 Leonid Vasilyev, Florin Adrian Radu, published by Ovidius University of Constanta
This work is licensed under the Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 License.