Biyarov, B. N. (2014) β€œOn Volterra Relatively Compact Perturbations of the \( \text{Laplace operator} \)”, Eurasian Mathematical Journal, 5(1), pp. 135–140. Available at: https://emj.enu.kz/index.php/main/article/view/566 (Accessed: 9 October 2025).