Luchka T. F., and Luchka A. Yu. “Development of Direct Methods of Mathematical Physics in Works by M. P. Kravchuk”. Ukrains’kyi Matematychnyi Zhurnal 44, no. 7 (August 3, 1992): 931-939. Accessed October 6, 2024. https://umj.imath.kiev.ua/index.php/umj/article/view/8126.