1. W. C. Holland, “A survey of varieties of ordered groups,” inUniversal Algebra and Lattice Theory, Lect. Notes. Math.,1004, Springer-Verlag, Berlin, 153–158 (1982).
2. “Problem lists, Ordered algebraic structures,”Not. Am. Math. Soc.,29, No. 40, 327 (1982).
3. Lattice Ordered Groups, Advances and Techniques, A. M. Glass and W. C. Holland (eds.), Kluwer, Dordrecht (1989).
4. N. Ya. Medvedev, “The lattices of varieties of lattice-ordered groups and Lie algebras,”Algebra Logika,16, No. 1, 40–45 (1977).
5. K. R. Pierce, “Amalgamations of lattice ordered gorups,”Trans. Am. Math. Soc.,172, No. 445, 249–260 (1972).