1. Birkhoff, G.,Lattice theory. Amer. Math. Soc. Colloq. Pub., 3rd Ed., 1973.
2. Fuchs, L.,Partially Ordered Algebraic Systems. Pergamon Press, 1963.
3. Holland, W. C.,Intrinsic metrics for lattice ordered groups. Alg. Universalis19 (1984), 142?150.
4. Jakubik, J.,On isometries of non-abelian lattice ordered groups. Math. Slovaca31 (1981), 171?175.
5. Jakubik, J.,Weak isometries of lattice ordered groups. Math. Slovaca38(1988), 133?138.