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Israel Journal of Mathematics
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https://dx.doi.org/10.48550/ar...
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Quite free complicated abelian groups, pcf and black boxes

Authors: Shelah, Saharon;

Quite free complicated abelian groups, pcf and black boxes

Abstract

We like to build Abelian groups (or R-modules) which on the one hand are quite free, say $\aleph_{��+ 1}$-free, and on the other hand, are complicated in suitable sense. We choose as our test problem having no non-trivial homomorphism to $Z$ (known classically for $\aleph_1$-free, recently for $\aleph_n$-free). We succeed to prove the existence of even $\aleph_{��_1 \cdot n}-$free ones. This requires building n-dimensional black boxes, which are quite free. Thus combinatorics is of self interest and we believe will be useful also for other purposes. On the other hand, modulo suitable large cardinals, we prove that it is consistent that every $\aleph_{��_1 \cdot ��}$-free Abelian group has non-trivial homomorphisms to Z.

Keywords

Large cardinals, 03E04, 03E75, 20K20, 20K30, black box, hereditary domain, Mathematics - Logic, Torsion-free groups, infinite rank, pcf, Ordered sets and their cofinalities; pcf theory, forcing, FOS: Mathematics, Applications of set theory, TDC\(_\lambda\), coslender group, Consistency and independence results, \(\lambda\)-free group, Whitehead group, Logic (math.LO)

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selected citations
These citations are derived from selected sources.
This is an alternative to the "Influence" indicator, which also reflects the overall/total impact of an article in the research community at large, based on the underlying citation network (diachronically).
BIP!Citations provided by BIP!
popularity
This indicator reflects the "current" impact/attention (the "hype") of an article in the research community at large, based on the underlying citation network.
BIP!Popularity provided by BIP!
influence
This indicator reflects the overall/total impact of an article in the research community at large, based on the underlying citation network (diachronically).
BIP!Influence provided by BIP!
impulse
This indicator reflects the initial momentum of an article directly after its publication, based on the underlying citation network.
BIP!Impulse provided by BIP!
4
Top 10%
Average
Average
Green