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arXiv · 1111.3485

Writing units of integral group rings of finite abelian groups as a product of Bass units

Eric Jespers·Ángel del Río·Inneke Van Gelder
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Abstract

We give a constructive proof of the theorem of Bass and Milnor saying that if $G$ is a finite abelian group then the Bass units of the integral group ring $\Z G$ generate a subgroup of finite index in its units group $\U(\Z G)$. Our proof provides algorithms to represent some units that contribute to only one simple component of $\Q G$ and generate a subgroup of finite index in $\U(\Z G)$ as product of Bass units. We also obtain a basis $B$ formed by Bass units of a free abelian subgroup of finite index in $\U(\Z G)$ and give, for an arbitrary Bass unit $b$, an algorithm to express $b^{\varphi(|G|)}$ as a product of a trivial unit and powers of at most two units in this basis $B$.

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Eric Jespers, Ángel del Río, Inneke Van Gelder. 2011-11-15. Writing units of integral group rings of finite abelian groups as a product of Bass units. https://arxiv.org/abs/1111.3485

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