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MATHEMATICA BOHEMICA, Vol. 133, No. 1, pp. 9-17 (2008)
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Non-singular covers over monoid rings

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Ladislav Bican

* Ladislav Bican*, Charles University, Faculty of Mathematics and Physics, Sokolovska 83, 186 75 Praha 8-Karlin, Czech Republik, e-mail: ` bican@karlin.mff.cuni.cz`

**Abstract:** We shall introduce the class of strongly cancellative multiplicative monoids which contains the class of all totally ordered cancellative monoids and it is contained in the class of all cancellative monoids. If $G$ is a strongly cancellative monoid such that $hG\subseteq Gh$ for each $h\in G$ and if $R$ is a ring such that $aR\subseteq Ra$ for each $a\in R$, then the class of all non-singular left $R$-modules is a cover class if and only if the class of all non-singular left $RG$-modules is a cover class. These two conditions are also equivalent whenever we replace the strongly cancellative monoid $G$ by the totally ordered cancellative monoid or by the totally ordered group.

**Keywords:** hereditary torsion theory, torsion theory of finite type, Goldie's torsion theory, non-singular module, non-singular ring, monoid ring, precover class, cover class

**Classification (MSC2000):** 16S90, 18E40, 16D80

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