1. Yu. L. Ershov, “Elementary group theories,” Dokl. Akad. Nauk SSSR, 203, No. 6, 1240–1243 (1972).
2. V. A. Roman’kov, “Universal theory of nilpotent groups,” Mat. Zametki., 25, No. 4, 487–495 (1979).
3. A. A. Mishchenko, “Universal equivalence of partially commutative class two nilpotent $ \mathbb{Q} $ -group,” Vestnik Omsk Univ., Special iss. (2008), pp. 93–100.
4. E. I. Timoshenko, “Universal equivalence of partially commutative metabelian groups,” Algebra Logika, 49, No. 2, 263–290 (2010).
5. A. Myasnikov and V. N. Remeslennikov, “Isomorphisms and elementary properties of nilpotent exponential groups,” Dokl. Akad. Nauk SSSR, 258, No. 5, 1056–1059 (1981).