Yesbayev, A.N., and M.N. Ospanov. “The Solvability Conditions for the Second Order Nonlinear Differential Equation With Unbounded Coefficients in L2(R)”. Bulletin of the Karaganda University. Mathematics Series 101, no. 1 (March 30, 2021): 104–110. Accessed July 10, 2025. http://mts.buketov.edu.kz/index.php/mathematics-vestnik/article/view/433.