Subject
Algebra and Number Theory
Reference3 articles.
1. Free Lie algebras and free groups;Baumslag;J. London Math. Soc.,1972
2. Finitely generated normal subgroups of polynilpotent groups;Eidel'kind;Siberian Math. J.,1968
3. Subgroups of free groups;Schreier;Abh. Math. Sem. Univ. Hamburg,1927