Berngardt, O. and Voronov, A. (2003) “A least squares method for sums of functions satisfying the differential equations with polynomial coefficients”, Numerical Methods and Programming (Vychislitel’nye Metody i Programmirovanie), 4(4), pp. 167–171. Available at: https://en.num-meth.ru/index.php/journal/article/view/85 (Accessed: 14 December 2025).