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Abelian Groups - László Fuchs [Springer]

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572 14 Butler <strong>Groups</strong><br />

in sharpening this result to five generators; they use free groups with distinguished subgroups to<br />

derive their result. The same paper contains several results on Butler groups with finite typesets.<br />

Blagoveshchenskaya–Göbel–Strüngmann [1] investigate a new class of groups: epic images of<br />

local almost completely decomposable groups. A generalization of near-isomorphism to infinite<br />

ranks is used as the basis of classification.<br />

Exercises<br />

(1) Any direct decomposition of the group G in the proof of Theorem 9.3 has only<br />

a finite number of summands ¤ 0.<br />

(2) Every endomorphism of G in Theorem 9.3 is determined by its action on A 00 .<br />

(3) Prove that the groups H X referred to in Theorem 9.1 are B 2 -groups. [Hint: they<br />

are finite sums of B 2 -groups tensored by free groups.]<br />

Problems to Chapter 14<br />

PROBLEM 14.1 (Metelli). Find invariants for the quasi-isomorphy classes of<br />

B .n/ -groups, especially in the n D 2 case.<br />

PROBLEM 14.2. Determine the projective dimensions of finite rank Butler<br />

groups over their endomorphism rings.<br />

PROBLEM 14.3. When is the tensor product of two B 1 -groups again a B 1 -group?<br />

PROBLEM 14.4. When is a finitely Butler group a B 2 -group? Is it if it has a solid<br />

chain?<br />

PROBLEM 14.5. Characterize inverse limits of (finite rank) Butler groups.

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