Using Goursat’s lemma for groups, a simple representation and the invariant factor decompositionsof the subgroups of the group $\mathbb{Z}_m \times \mathbb{Z}_n$ are deduced, where $m$ and $n$ are arbitrarypositive integers. As consequences, explicit formulas for the total number of subgroups,the number of subgroups with a given invariant factor decomposition, and the number ofsubgroups of a given order are obtained.
@article{335, title = {Subgroups of finite Abelian groups having rank two via Goursat's lemma}, journal = {Tatra Mountains Mathematical Publications}, volume = {58}, year = {2014}, doi = {10.2478/tatra.v59i0.335}, language = {EN}, url = {http://dml.mathdoc.fr/item/335} }
Tóth, László. Subgroups of finite Abelian groups having rank two via Goursat’s lemma. Tatra Mountains Mathematical Publications, Tome 58 (2014) . doi : 10.2478/tatra.v59i0.335. http://gdmltest.u-ga.fr/item/335/