On countable extensions of primary abelian groups

Danchev, P. V.

Archivum mathematicum, Tome 43 (2007) no. 1, pp. 61-66.

Résumé

It is proved that if $A$ is an abelian $p$-group with a pure subgroup $G$ so that $A/G$ is at most countable and $G$ is either $p^{\omega +n}$-totally projective or $p^{\omega +n}$-summable, then $A$ is either $p^{\omega +n}$-totally projective or $p^{\omega +n}$-summable as well. Moreover, if in addition $G$ is nice in $A$, then $G$ being either strongly $p^{\omega +n}$-totally projective or strongly $p^{\omega +n}$-summable implies that so is $A$. This generalizes a classical result of Wallace (J. Algebra, 1971) for totally projective $p$-groups as well as continues our recent investigations in (Arch. Math. (Brno), 2005 and 2006). Some other related results are also established.

Détail

Classification : 20K10, 20K15
Keywords: countable quotient groups; $\omega $-elongations; $p^{\omega +n}$-totally projective groups; $p^{\omega +n}$-summable groups