SADYBEKOV, M.; TURMETOV, B. On analogues of periodic boundary value problems for the Laplace operator in a ball. Eurasian Mathematical Journal, [S. l.], v. 3, n. 1, p. 143–146, 2012. Disponível em: https://emj.enu.kz/index.php/main/article/view/785. Acesso em: 31 oct. 2025.