Kabanikhin, S., and M. Shishlenin. “Multidimensional Analogues of Gelfand–Levitan, Marchenko and Krein Equations. Theory, Numerics and Applications”. Journal of Mathematics, Mechanics and Computer Science, vol. 86, no. 3, Sept. 2018, pp. 63-69, https://bm.kaznu.kz/index.php/kaznu/article/view/498.