1. A. Arhangel’skii and M. Tkachenko, Topological Groups and Related Structures, Atlantis Studies in Mathematics, Vol. 1, Atlantis Press, Paris; World Scientific, Hackensack, NJ, 2008.
2. T. Banakh, Cardinal characteristics of the ideal of Haar null sets, Commentationes Mathematicae Universitatis Carolinae 45 (2004), 119–137.
3. T. Banakh, Haar-open sets: a right way of generalizing the Steinhaus sum theorem to non-locally compact groups, preprint,
https://doi.org/arxiv.org/abs/1805.07515
.
4. T. Banakh, S. Glab, E. Jablońska and J. Swaczyna, Haar-I sets: looking at small sets in Polish groups through compact glasses, preprint,
https://doi.org/arxiv.org/abs/1803.06712
.
5. K. Baron and R. Ger, Problem (P239), in The 21st International Symposium on Functional Equations, August 6–13, 1983, Konolfingen, Switzerland, Aequationes Mathematicae 26 (1984), 225–294.