Banakh, T. O., I. V. Protasov, and K. D. Protasova. 2017. “Descriptive Complexity of the Sizes of Subsets of groups”. Ukrains’kyi Matematychnyi Zhurnal 69 (9), 1280-83. https://umj.imath.kiev.ua/index.php/umj/article/view/1780.