Hostname: page-component-cd9895bd7-fscjk Total loading time: 0 Render date: 2024-12-24T18:29:25.375Z Has data issue: false hasContentIssue false

A note on rank and direct decompositions of torsion-free Abelian groups. II

Published online by Cambridge University Press:  24 October 2008

A. L. S. Corner
Affiliation:
Worcester College, Oxford

Extract

According to well-known theorems of Kaplansky and Baer–Kulikov–Kapla nsky–Fuchs (4, 2), the class of direct sums of countable Abelian groups and the class of direct sums of torsion-free Abelian groups of rank 1 are both closed under the formation of direct summands. In this note I give an example to show that the class of direct sums of torsion-free Abelian groups of finite rank does not share this closure property: more precisely, there exists a torsion-free Abelian group G which can be written both as a direct sum G = A⊕B of 2 indecomposable groups A, B of rank ℵ0 and as a direct sum G = ⊕n ε zCn of ℵ0 indecomposable groups Cn (nεZ) of rank 2, where Z is the set of all integers.

Type
Research Article
Copyright
Copyright © Cambridge Philosophical Society 1969

Access options

Get access to the full version of this content by using one of the access options below. (Log in options will check for institutional or personal access. Content may require purchase if you do not have access.)

References

REFERENCES

(1)Corner, A. L. S.A note on rank and direct decompositions of torsion-free Abelian groups. Proc. Cambridge Philos. Soc. 57 (1961), 230233.CrossRefGoogle Scholar
(2)Fuchs, L.Notes on Abelian groups, I. Ann. Univ. Sci. Budapest. Eötvös Sect. Math. 2 (1959), 523.Google Scholar
(3)Jónsson, B.On direct decompositions of torsion-free Abelian groups. Math. Scand. 5 (1957), 230235.CrossRefGoogle Scholar
(4)Kaplansky, I.Projective modules. Ann. of Math. 68 (1958), 372377.CrossRefGoogle Scholar