[2] Paul Conrad:
Epi-archimedean groups. Czech. Math. Journal, 24 (99), (1974) 192-218.
MR 0347701
[3] Paul Conrad: Lattice-ordered Groups. Tulane University, 1970.
[4] Laszlo Fuchs:
Partially Ordered Algebraic Systems. Pergamon Press, Addison Wesley, New York 1963.
MR 0171864
[5] Jorge Martinez:
Free products of abelian $l$-groups. Czech. Math. Journal, 23 (98), (1973), 349-361,
MR 0371770
[6] Jorge Martinez:
Torsion theory for lattice-ordered groups. Czech. Math. Journal 25 (100), (1975), 284-299.
MR 0389705