Ptashnik, B. I., and S. M. Repetylo. “Boundary-Value Problem With Mixed Conditions for Linear Typeless Partial Differential Equations”. Ukrains’kyi Matematychnyi Zhurnal 68, no. 5 (May 25, 2016): 665-682. Accessed April 23, 2024. https://umj.imath.kiev.ua/index.php/umj/article/view/1870.