1. A. I. Shirshov, “On free Lie rings,” Matem. Sb.,45, No. 2, 113–122 (1958).
2. A. I. Shirshov, “Subalgebras of free Lie algebras,” Matem. Sb.,33, No. 2, 441–452 (1953).
3. E. Witt, “Die Unterringe der freien Lieschen Ringe,” Math. Z.,64, No. 2, 195–216 (1956).
4. A. I. Shirshov, “Subalgebras of free commutative and of free anticommutative algebras,” Matem. Sb.,34, No. 1, 81–88 (1954).
5. A. G. Kurosh, “Nonassociative free algebras and free products of algebras,” Matem. Sb.,20, No. 2, 239–262 (1947).