1. J. Martinez, "Varieties of lattice-ordered groups," Math. Z.,137, No. 4, 265–284 (1974).
2. H. Neumann, Varieties of Groups, Springer-Verlag (1967).
3. G. D. Birkhoff, Lattice Theory, Amer. Math. Soc. (1967).
4. A. Yu. Ol'shanskii, "On the problem of a finite basis of identities in groups," Izv. Akad. Nauk SSSR, Ser. Mat.,34, No. 2, 316–384 (1970).
5. D. M. Smirnov, "Generalized solvable groups and their group rings," Mat. Sb.,67, 366–383 (1965).