BARANNYK, A. F.; BARANNIK, L. F.; FUSHCHICH, V. I. Reduction of the multidimensional d’Alembert equation to two-dimensional equations. Ukrains’kyi Matematychnyi Zhurnal, [S. l.], v. 46, n. 6, p. 651–662, 1994. Disponível em: https://umj.imath.kiev.ua/index.php/umj/article/view/5692. Acesso em: 5 dec. 2025.