O. F. Gerus, “An estimate for the modulus of continuity of a quaternion singular Cauchy integral”, Ukr. Mat. Zhurn., vol. 62, no. 10, pp. 1428–1435, Oct. 2010, Accessed: Dec. 05, 2025. [Online]. Available: https://umj.imath.kiev.ua/index.php/umj/article/view/2967