24.11.2017 Views

Abelian Groups - László Fuchs [Springer]

Create successful ePaper yourself

Turn your PDF publications into a flip-book with our unique Google optimized e-Paper software.

548 14 Butler <strong>Groups</strong><br />

it clear: countable Butler groups are not necessarily pure subgroups in completely decomposable<br />

groups. Indeed, Arnold–Rangaswamy [1] give an example of a countable rank Butler group that<br />

fails to be a pure subgroup in any completely decomposable group.<br />

Exercises<br />

(1) The union of a chain of pure finitely Butler subgroups is also finitely Butler.<br />

(2) A TEP-subgroup in a B 2 -group is a B 2 -group.<br />

(3) (Bican–El Bashir) Let A be a torsion-free group, and A D B C C where B; C are<br />

B 1 -groups. If B \ C is TEP in B,thenA is also a B 1 -group.<br />

(4) Let 0 D G 0 < G 1 < < G n < ::: be a countable chain of countable Butler<br />

groups such that each link is pure in the next one. Then the union G D S n

Hooray! Your file is uploaded and ready to be published.

Saved successfully!

Ooh no, something went wrong!