BanakhT. O., ProtasovI. V., and SlobodianiukS. V. “Scattered Subsets of Groups”. Ukrains’kyi Matematychnyi Zhurnal, Vol. 67, no. 3, Mar. 2015, pp. 304-12, https://umj.imath.kiev.ua/index.php/umj/article/view/1983.