V. V. Volchkov, “On the Pompeiu problem and its generalizations”, Ukr. Mat. Zhurn., vol. 45, no. 10, pp. 1444–1448, Oct. 1993, Accessed: Feb. 16, 2026. [Online]. Available: https://umj.imath.kiev.ua/index.php/umj/article/view/5949