Kopach, M.I., A.F. Obshta, and B.A. Shuvar. 2010. “An Application of Analogues of Two-Sided Kurpel’s Methods to Ordinary Differential Equations”. Carpathian Mathematical Publications 2 (2):48-54. https://vps.pnu.edu.ua/index.php/cmp/article/view/3966.