[1] N. Ya. Medvedev: On the lattice of $o$-approximable $\ell $-varieties. Czech. Math. J. 34 (109) (1984), 6–17. (Russian) MR 0731975

[2] V. M. Kopytov, N. Ya. Medvedev: The Theory of Lattice-Ordered Groups. Kluwer Academic Publishers, Dordrecht-Boston-London, 1994. MR 1369091

[3] V. M. Kopytov: Lattice-Ordered Groups. Moscow, Nauka, 1984. (Russian) MR 0806956 | Zbl 0567.06011

[4] M. I. Kargapolov, Yu. I. Merzlyakov: Fundamentals of the Theory of Groups. Springer, Berlin, 1979. MR 0551207

[5] A. G. Kurosh: Theory of Groups. Moscow, Nauka, 1967. (Russian) MR 0249495

[6] M. E. Huss, N. R. Reilly: On reversing the order of a lattice-ordered group. J. Algebra 9 (1984), 176–191. DOI 10.1016/0021-8693(84)90133-9 | MR 0765778

[7] M. Anderson, M. Darnel, T. Feil: A variety of lattice-ordered groups containing all representable covers of the abelian variety. Order 7 (1991), 401–405. DOI 10.1007/BF00383204 | MR 1120986

[8] S. V. Molochko, S. V. Morozova: On the theory of varieties of lattice-ordered groups. Sib. Math. J. 38, N 1 (1997), 151–160. (Russian) MR 1446681