1. Poroshenko E. N., “Commutator width of elements in a free metabelian Lie algebra,” Algebra and Logic, 53, No. 5, 377–396 (2014).
2. Roman’kov V. A., “Unsolvability of the endomorphic reducibility problem in free nilpotent groups and in free rings,” Algebra and Logic, 16, No. 4, 310–320 (1977).
3. Allambergenov Kh. S. and Roman’kov V. A., “On a product of commutators in groups,” Submitted to VINITI, Sib. Mat. Zh., Novosibirsk, 1985. No. 4566–85.
4. Allambergenov Kh. S. and Roman’kov V. A., “Products of commutators in groups,” Dokl. Akad. Nauk UzSSR, 4, 14–15 (1984).
5. Akhavan-Malayeri M. and Rhemtulla A., “Commutator length of abelian-by-nilpotent groups,” Glasgow Math. J., 40, 117–121 (1998).