Y. I. . Melnik, “Inverse theorems of approximation of regular (in convex polygons) functions by exponential polynomials in the integral metric”, Ukr. Mat. Zhurn., vol. 40, no. 6, pp. 751–757, Nov. 1988, Accessed: Dec. 06, 2025. [Online]. Available: https://umj.imath.kiev.ua/index.php/umj/article/view/9285