Оrосhkо Y. В. On the powers of an operator of an engendered Cauchy problem for a hyperbolic equation of the second order. Ukrains’kyi Matematychnyi Zhurnal, [S. l.], v. 18, n. 4, p. 34–48, 1966. Disponível em: https://umj.imath.kiev.ua/index.php/umj/article/view/8311. Acesso em: 15 dec. 2025.