BUDOCHKINA, S. A.; SAVCHIN, V. M. On direct variational formulations for second order evolutionary equations. Eurasian Mathematical Journal, [S. l.], v. 3, n. 4, p. 23–34, 2012. Disponível em: https://emj.enu.kz/index.php/main/article/view/804. Acesso em: 31 oct. 2025.