PTASHNIK, B. I.; SYMOTYUK, M. M. Multipoint Problem for Nonisotropic Partial Differential Equations with Constant Coefficients. Ukrains’kyi Matematychnyi Zhurnal, [S. l.], v. 55, n. 2, p. 241–254, 2003. Disponível em: https://umj.imath.kiev.ua/index.php/umj/article/view/3902. Acesso em: 5 dec. 2025.