Кузишин, Іванна Ярославівна. “PERIODICITY OF SOLUTIONS TO LINEAR SYSTEMS OF ORDINARY DIFFERENTIAL EQUATIONS WITH PERTUBATION”. PRECARPATHIAN BULLETIN OF THE SHEVCHENKO SCIENTIFIC SOCIETY. Number, no. 1(29), Feb. 2019, pp. 90-94, https://pvntsh.nung.edu.ua/index.php/number/article/view/143.