BURGUMBAYEVA, S. The tri-harmonic Neumann problem. Bulletin of the Karaganda University. Mathematics Series, [S. l.], v. 92, n. 4, p. 29–37, 2018. DOI: 10.31489/2018m4/29-37. Disponível em: https://mts.buketov.edu.kz/index.php/mathematics-vestnik/article/view/236. Acesso em: 31 aug. 2025.