A. A. Shumeiko, “On approximation of functions from below by splines of the best approximation with free nodes”, Ukr. Mat. Zhurn., vol. 52, no. 4, pp. 512–523, Apr. 2000, Accessed: Dec. 05, 2025. [Online]. Available: https://umj.imath.kiev.ua/index.php/umj/article/view/4440