$Bext^2(G,T)$ can be nontrivial, even assuming GCH
by Magidor and Shelah. [MgSh:514]
Abelian group theory and related topics, 1994
Using the consistency of some large cardinals we produce a
model of Set Theory in which the generalized continuum
hypothesis holds and for some torsion-free abelian group G
of
cardinality aleph_{omega +1} and for some torsion group T,
Bext^2(G,T)
not =0 .
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