Authors
S. Cheresharov
Faculty of Mathematics and Informatics, Plovdiv University “Paisii Hilendarski”, Plovdiv, Bulgaria
H. Krushkov
Faculty of Mathematics and Informatics, Plovdiv University “Paisii Hilendarski”, Plovdiv, Bulgaria
S. Stoyanov
Faculty of Mathematics and Informatics, Plovdiv University “Paisii Hilendarski”, Plovdiv, Bulgaria
I. Popchev
Faculty of Economics and Social Sciences, University of Plovdiv “Paisii Hilendarski”, Bulgaria
