Luchka , T.F. and Luchka , A.Y. (1992) “Development of direct methods of mathematical physics in works by M. P. Kravchuk”, Ukrains’kyi Matematychnyi Zhurnal, 44(7), pp. 931–939. Available at: https://umj.imath.kiev.ua/index.php/umj/article/view/8126 (Accessed: 6 December 2025).