Shukurov, Aydin Shukur. “On the Number of Non-Real Eigenvalues of the Sturm-Liouville Problem”. Eurasian Mathematical Journal 8, no. 3 (September 30, 2017): 77–84. Accessed September 18, 2025. https://emj.enu.kz/index.php/main/article/view/673.