VASYLYSHYN, P. B.; KLYUS, I. S.; PTASHNIK, B. I. Multipoint problem for hyperbolic equations with variable coefficients. Ukrains’kyi Matematychnyi Zhurnal, [S. l.], v. 48, n. 11, p. 1468–1476, 1996. Disponível em: https://umj.imath.kiev.ua/index.php/umj/article/view/5200. Acesso em: 5 dec. 2025.