B. I. Ptashnik and S. M. Repetylo, “Boundary-value problem with mixed conditions for linear typeless partial differential equations”, Ukr. Mat. Zhurn., vol. 68, no. 5, pp. 665–682, May 2016, Accessed: Dec. 05, 2025. [Online]. Available: https://umj.imath.kiev.ua/index.php/umj/article/view/1870