SHKLYAR, A. Ya. Well-posedness of the cauchy problem for complete second-order operator-differential equations. Ukrains’kyi Matematychnyi Zhurnal, [S. l.], v. 48, n. 7, p. 999–1006, 1996. Disponível em: https://umj.imath.kiev.ua/index.php/umj/article/view/5272. Acesso em: 11 apr. 2025.