JENALIYEV, M.T.; SERIK, A.M. On the spectral problem for three-dimesional bi-Laplacian in the unit sphere. Bulletin of the Karaganda University. Mathematics Series, [S. l.], v. 114, n. 2, p. 86–104, 2024. DOI: 10.31489/2024m2/86-104. Disponível em: http://mts.buketov.edu.kz/index.php/mathematics-vestnik/article/view/636. Acesso em: 25 aug. 2025.