Краснодембський, Адам Михайлович. “PERIODICITY OF DECISIONS OF SOME SYSTEM OF TWO NONLINEAR DIFFERENTIAL EQUALIZATIONS OF THE SECOND ORDER”. PRECARPATHIAN BULLETIN OF THE SHEVCHENKO SCIENTIFIC SOCIETY. Number, no. 1(9), Mar. 2019, pp. 21-25, https://pvntsh.nung.edu.ua/index.php/number/article/view/281.