Burenkov, Victor, and Mukhtarbai Otelbaev. “On the Singular Numbers of Correct Restrictions of Non-Selfadjoint Elliptic Differential Operators”. Eurasian Mathematical Journal 2, no. 1 (March 30, 2011). Accessed October 31, 2025. https://emj.enu.kz/index.php/main/article/view/75.