@article{Banakh_Protasov_Protasova_2017, title={Descriptive complexity of the sizes of subsets of
groups}, volume={69}, url={https://umj.imath.kiev.ua/index.php/umj/article/view/1780}, abstractNote={We study the Borel complexity of some basic families of subsets of a countable group (large, small, thin, rarefied, etc.)
determined by the sizes of their elements. The obtained results are applied to the Czech – Stone compactification $\beta G$ of the
group $G$. In particular, it is shown that the closure of the minimal ideal $\beta G$ has the $F_{\sigma \delta}$ type.}, number={9}, journal={Ukrains’kyi Matematychnyi Zhurnal}, author={Banakh, T. O. and Protasov, I. V. and Protasova, K. D.}, year={2017}, month={Sep.}, pages={1280-1283} }