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[2] Hall P.: Nilpotent Groups. Canadian Mathematical Congress Summer Seminar. University of Alberta. 1957.

[3] Kurosh A. G.: The theory of groups. Chelsea Publishing Company 1955. MR 0109842

[4] Neumann B. H.: Ascending derived series. Compositio Mathematica 13 (1956). 47-64. MR 0089196 | Zbl 0070.25405