Precovers and Goldie's torsion theory

L Bican - Mathematica Bohemica, 2003 - dml.cz
L Bican
Mathematica Bohemica, 2003dml.cz
Recently, Rim and Teply, using the notion of $\tau $-exact modules, found a necessary
condition for the existence of $\tau $-torsionfree covers with respect to a given hereditary
torsion theory $\tau $ for the category $ R $-mod of all unitary left $ R $-modules over an
associative ring $ R $ with identity. Some relations between $\tau $-torsionfree and $\tau $-
exact covers have been investigated in. The purpose of this note is to show that if
$\sigma=(\mathcal T_ {\sigma},\mathcal F_ {\sigma}) $ is Goldie's torsion theory and …
Recently, Rim and Teply , using the notion of -exact modules, found a necessary condition for the existence of -torsionfree covers with respect to a given hereditary torsion theory for the category -mod of all unitary left -modules over an associative ring with identity. Some relations between -torsionfree and -exact covers have been investigated in . The purpose of this note is to show that if is Goldie’s torsion theory and is a precover class, then is a precover class whenever . Further, it is shown that is a cover class if and only if is of finite type and, in the case of non-singular rings, this is equivalent to the fact that is a cover class for all hereditary torsion theories .
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