É. M. Zhmud, “On finite groups all irreducible characters of which take at most two nonzero values”, Ukr. Mat. Zhurn., vol. 47, no. 8, pp. 1144–1148, Aug. 1995, Accessed: Dec. 05, 2025. [Online]. Available: https://umj.imath.kiev.ua/index.php/umj/article/view/5512