Authors
Emil Hadzhikolev
Plovdiv University “Paisii Hilendarski”, Department of Mathematics and Informatics, Bulgaria
Stanka Hadzhikoleva
Plovdiv University “Paisii Hilendarski”, Department of Mathematics and Informatics, Bulgaria
© 2019 Emil Hadzhikolev, Stanka Hadzhikoleva, published by Lucian Blaga University of Sibiu
This work is licensed under the Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 License.