1. D. O. Cutler, On the structure of primary abelian groups with countable Ulm type, Trans. Amer. Math. Soc., 152(3), 503–518 (1970).
2. P. V. Danchev, Commutative group algebras of abelian Σ-groups, Math. J. Okayama Univ., 40(2), 77–90 (1998).
3. P. V. Danchev, Theorems of the type of Nunke for abelian groups, Compt. Rend. Acad. Bulg. Sci., 53(10), 5–8 (2000).
4. P. V. Danchev, Characteristic properties of large subgroups in primary abelian groups, Proc. Indian Acad. Sci. Math. Sci., 114(3), 225–233 (2004).
5. P. V. Danchev, Primary abelian Σ-groups of countable length ⩾ ω.2 are not necessarily summable, Comment. Math. Univ. St. Paul., 53(2), 115–119 (2004).