Zelenyak , T.I. (1992) “Concerning the use of variational methods in the theory of parabolic equations ”, Ukrains’kyi Matematychnyi Zhurnal, 44(9), pp. 1284–1287. Available at: https://umj.imath.kiev.ua/index.php/umj/article/view/8183 (Accessed: 5 December 2025).