KHOMA, N. H. Linear periodic boundary-value problem for a second-order hyperbolic equation. I. Ukrains’kyi Matematychnyi Zhurnal, [S. l.], v. 50, n. 11, p. 1537–1544, 1998. Disponível em: https://umj.imath.kiev.ua/index.php/umj/article/view/4806. Acesso em: 11 apr. 2025.