Vlasii OD, Ptashnik BI. Nonlocal boundary-value problem for linear partial differential equations unsolved with respect to the higher time derivative. Ukr. Mat. Zhurn. [Internet]. 2007Mar.25 [cited 2024Nov.22];59(3):370–381. Available from: https://umj.imath.kiev.ua/index.php/umj/article/view/3313