KRITSKOV, L.V.; SADYBEKOV, M.A.; SARSENBI, A.M. Nonlocal spectral problem for a second-order differential equation with an involution. Bulletin of the Karaganda University. Mathematics Series, [S. l.], v. 91, n. 3, p. 53–60, 2018. DOI: 10.31489/2018m3/53-60. Disponível em: https://mts.buketov.edu.kz/index.php/mathematics-vestnik/article/view/243. Acesso em: 16 sep. 2025.