Authors
Fariba Fattahi
Department of Mathematics, University of Mazandaran,, Babolsar, Iran
Mohsen Alimohammady
Department of Mathematics, University of Mazandaran,, Babolsar, Iran
© 2017 Fariba Fattahi, Mohsen Alimohammady, published by Ovidius University of Constanta
This work is licensed under the Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 License.