PtashnikB. I., and SymotyukM. M. “Multipoint Problem for Nonisotropic Partial Differential Equations With Constant Coefficients”. Ukrains’kyi Matematychnyi Zhurnal 55, no. 2 (February 25, 2003): 241-254. Accessed July 27, 2024. https://umj.imath.kiev.ua/index.php/umj/article/view/3902.