1. R. N. Ball, Full convex ℓ-subgroups of a lattice-ordered group, Ph.D. Thesis, University of Wisconsin, Madison, Wis., USA, 1974.
2. R. N. Ball and M. Droste, Normal subgroups of doubly transitive automorphism groups of chains, Trans. Amer. Math. Soc. 290 (1985), 647–664.
3. M. R. Darnel, M. Giraudet, and S. H. McCleary, Uniqueness of the group operation on the lattice of order-automorphisms of the real line, Algebra Universalis 33 (1995), 419–427.
4. M. Droste, Representations of free lattice-ordered groups, Order 10(1993), 375– 381.
5. M. Droste and S. H. McCleary, The root system of prime subgroups of a free lattice-ordered group (without GCH), Order 6 (1989), 305–309.