1. R. Baer, Die Torsionsuntergruppe einer abelschen Gruppe, Mathematische Annalen 135(1979), 219–234
2. S.U. Chase, On direct sums and products of modules, Pacific Journal of Math. 12(1962), 847–854
3. M. Dugas and B. Zimmermann-Huisgen, Iterated direct Sums and Products of Modules, this volume
4. L. Fuchs, Abelian groups, Publ. House of the Acad. Sci, Budapest 1958
5. L. Fuchs, Infinite abelian groups, Academic Press, New York, Vol.1(1970), Vol.2(1973); R.uss. transl.: Л.Фукс, Бесконечные абелевы группы, том 1, Москва 1974, том 2, Москва 1977