MURATBEKOV, M.B.; IGISINOV, S.Zh. On closability and bounded invertibility of mixed type differential operator in an unbounded domain. Bulletin of the Karaganda University. Mathematics Series, [S. l.], v. 78, n. 2, p. 106–112, 2015. Disponível em: http://mts.buketov.edu.kz/index.php/mathematics-vestnik/article/view/30. Acesso em: 7 sep. 2025.