Square subgroups of rank two abelian groups
A. M. Aghdam, A. Najafizadeh (2009)
Colloquium Mathematicae
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Let G be an abelian group and ◻ G its square subgroup as defined in the introduction. We show that the square subgroup of a non-homogeneous and indecomposable torsion-free group G of rank two is a pure subgroup of G and that G/◻ G is a nil group.