Vlasii, O.D. and Ptashnik, B.I. (2003) “A Problem with Nonlocal Conditions for Partial Differential Equations Unsolved with Respect to the Leading Derivative”, Ukrains’kyi Matematychnyi Zhurnal, 55(8), pp. 1022–1034. Available at: https://umj.imath.kiev.ua/index.php/umj/article/view/3978 (Accessed: 5 December 2025).