RECOGNIZABLE LANGUAGES AND FINITE SEMILATTICES OF GROUPS. Gérard Lallement, Elaine Milito (1975) Semigroup forum
Rings on certain classes of torsion-free Abelian groups Barry J. Gardner, David R. Jackett (1976) Commentationes Mathematicae Universitatis Carolinae
Rings on completely decomposable torsion-free Abelian groups Barry J. Gardner (1974) Commentationes Mathematicae Universitatis Carolinae