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A note on group algebras of p -primary abelian groups

William Ullery — 1995

Commentationes Mathematicae Universitatis Carolinae

Suppose p is a prime number and R is a commutative ring with unity of characteristic 0 in which p is not a unit. Assume that G and H are p -primary abelian groups such that the respective group algebras R G and R H are R -isomorphic. Under certain restrictions on the ideal structure of R , it is shown that G and H are isomorphic.

Quasi-balanced torsion-free groups

H. Pat GoetersWilliam Ullery — 1998

Commentationes Mathematicae Universitatis Carolinae

An exact sequence 0 A B C 0 of torsion-free abelian groups is quasi-balanced if the induced sequence 0 𝐐 Hom ( X , A ) 𝐐 Hom ( X , B ) 𝐐 Hom ( X , C ) 0 is exact for all rank-1 torsion-free abelian groups X . This paper sets forth the basic theory of quasi-balanced sequences, with particular attention given to the case in which C is a Butler group. The special case where B is almost completely decomposable gives rise to a descending chain of classes of Butler groups. This chain is a generalization of the chain of Kravchenko classes that arise from balanced...

Isotype subgroups of mixed groups

Charles K. MegibbenWilliam Ullery — 2001

Commentationes Mathematicae Universitatis Carolinae

In this paper, we initiate the study of various classes of isotype subgroups of global mixed groups. Our goal is to advance the theory of Σ -isotype subgroups to a level comparable to its status in the simpler contexts of torsion-free and p -local mixed groups. Given the history of those theories, one anticipates that definitive results are to be found only when attention is restricted to global k -groups, the prototype being global groups with decomposition bases. A large portion of this paper is...

Isotype knice subgroups of global Warfield groups

Charles K. MegibbenWilliam Ullery — 2006

Czechoslovak Mathematical Journal

If H is an isotype knice subgroup of a global Warfield group G , we introduce the notion of a k -subgroup to obtain various necessary and sufficient conditions on the quotient group G / H in order for H itself to be a global Warfield group. Our main theorem is that H is a global Warfield group if and only if G / H possesses an H ( 0 ) -family of almost strongly separable k -subgroups. By an H ( 0 ) -family we mean an Axiom 3 family in the strong sense of P. Hill. As a corollary to the main theorem, we are able to characterize...

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