BOBYK, I. O.; PTASHNIK, B. I. Boundary-value problems for hyperbolic equations with constant coefficients. Ukrains’kyi Matematychnyi Zhurnal, [S. l.], v. 46, n. 7, p. 795–802, 1994. Disponível em: https://umj.imath.kiev.ua/index.php/umj/article/view/5669. Acesso em: 6 dec. 2025.