1. V. N. Remeslennikov, ?Embedding theorems for pro-p-groups,? Izv. Akad. Nauk SSSR, Ser. Mat.,43, No. 2, 339?417 (1979).
2. H. Koch, Theory of Galois p-Extensions [Russian translation], Mir, Moscow (1973).
3. A. F. Krasnikov, ?On nilpotent subgroups of relatively free groups,? Algebra Logika,17, No. 4, 389?401 (1978).