1. J. Nielsen, ?Die Isomorphismen der allgemeinen unendlichen Gruppe mit zwei Erzeugenden,? Math. Ann., No. 7, 385?397 (1918).
2. W. Magnus, A. Karass, and D. Solitar, Combinatorial Group Theory, Interscience, New York (1966).
3. A. I. Mal'tsev, ?On the equation zxyx?1y?1z?1=aba?0b?1 in a free group,? Algebra i Logika,1, No. 5, 45?50 (1962).
4. A. F. Krasnikov, ?On the generating elements of the group F/[N, N],? Mat. Zametki,24, No. 2, 167?173 (1988).
5. V. N. Remeslennikov and V. G. Sokolov, ?Some properties of the Magnus embedding,? Algebra Logika,9, No. 5, 566?578 (1970).