1. H. Cartan and S. Eilenberg, Homological Algebra, Princeton Univ. Press, Princeton, NJ, 1956; Russian translation: Inostrannaya Literatura, Moscow, 1960.
2. S. MacLane, Homology, Springer-Verlag, Berlin, 1963; Russian translation: Mir, Moscow, 1966.
3. H. Zassenhaus, The Theory of Groups, New York, 1958.
4. A. L. Shmel’kin, “A remark to Shmel’kin’s paper “Wreath products and varieties of groups,” Izv. Akad. Nauk SSSR Ser. Mat. [Math. USSR-Izv.], 31 (1967), 443–444.
5. N. Blackburn, “Note on a theorem of Magnus,” J. Austral. Math. Soc., 10 (1969), 469–474.