ISHKIN, K. K.; MARVANOV, R. I. Non-accretive Sturm–Liouville operator with discrete spectrum. Journal of Mathematics, Mechanics and Computer Science, [S. l.], v. 108, n. 4, p. 18–25, 2020. DOI: 10.26577/JMMCS.2020.v108.i4.02. Disponível em: https://bm.kaznu.kz/index.php/kaznu/article/view/816. Acesso em: 22 jul. 2024.