ORUMBAYEVA, N.T.; KELDIBEKOVA, A.B. On the solvability of the duo-periodic problem for the hyperbolic equation system with a mixed derivative. Bulletin of the Karaganda University. Mathematics Series, [S. l.], v. 93, n. 1, p. 59–71, 2019. DOI: 10.31489/2019m1/59-71. Disponível em: http://mts.buketov.edu.kz/index.php/mathematics-vestnik/article/view/269. Acesso em: 3 sep. 2025.