Authors
Lhoussain El Fadil
Dept. of Math., Fac. of Sci. Dhar-El Mahraz, Sidi Mohamed Ben Abdellah University, Atlas-Fez, Morocco
© 2019 Lhoussain El Fadil, published by Slovak Academy of Sciences, Mathematical Institute
This work is licensed under the Creative Commons Attribution-NonCommercial-NoDerivatives 3.0 License.