1. Home Page
https://en.wikipedia.org/w/index.php?title=Special:ElectronPdf&page=Solvable+group&action=show-download-screen
2. Home Page
https://lektsii.org/13-61547.html
3. Serdyukova, N., Serdyukov, V.: Algebraic Formalization of Smart Systems. Theory and Practice, Smart Innovation, Systems and Technologies, SIST, vol. 91. Springer Nature, Switzerland (2018)
4. Olshansky, AYu., Shmelkin, A.L.: Infinite groups, Itogi Nauki i Tekhniki. Ser. Lying. prob. mat. Fundam. Directions 37, 5–113 (1989)
5. Mazhuga, A. M.: Verbally Closed Subgroups, Thesis for the Degree of Candidate of Physical and Mathematical Sciences. Moscow State University, Moscow (2018) (in Russian)