Ospanov, K.N., and Zh.B. Yeskabylova. “Conditions of Coercive Solvability of Third-Order Differential Equation With Unbounded Intermediate Coefficients”. Bulletin of the Karaganda University. Mathematics Series, vol. 94, no. 2, June 2019, pp. 56-69, doi:10.31489/2019m2/56-69.