1. Gruenberg K. W., “Residual properties of infinite soluble groups,” Proc. London Math. Soc., 7, 29–62 (1957).
2. Sokolov E. V., “A characterization of root classes of groups,” Comm. Algebra, 43, No. 2, 856–860 (2015); DOI: 10.1080/00927872.2013.851207.
3. Gol’tsov D. V. and Yatskin D. V., “Classes of groups and subgroup topologies,” Vestnik Ivanovsk. Gos. Univ. Ser. Estestv., Obshchestv. Nauki, No. 2, 115–128 (2011).
4. Azarov D. N. and Tieudjo D., “On root-class residuality of amalgamated free products,” Nauch. Tr. Ivanovsk. Gos. Univ., 5, 6–10 (2002).
5. Azarov D. N. and Gol’tsov D. V., “On the virtually residuality of generalized free products and HNN-extensions of groups by some classes of finite groups,” Vestnik Ivanovsk. Gos. Univ. Ser. Estestv., Obshchestv. Nauki, No. 2, 86–91 (2012).