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Andriy Styahar
Faculty of Applied Mathematics and Informatics, Department of Applied Mathematics, Ivan Franko Lviv National University, Universytetska,1, 79000, Lviv, Ukraine
Yarema Savula
Faculty of Applied Mathematics and Informatics, Department of Applied Mathematics, Ivan Franko Lviv National University, Universytetska,1, 79000, Lviv, Ukraine