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math.LO2001
Almost-free E-rings of cardinality aleph_1
Rüdiger Göbel, Saharon Shelah, Lutz Strüngmann
An E-ring is a unital ring R such that every endomorphism of the underlying abelian group R^+ is multiplication by some ring-element. The existence of almost-free E-rings of cardin…
math.LO2001
Some ugly aleph_1-free abelian groups
Saharon Shelah, Lutz Strüngmann
Given an aleph_1-free abelian group G we characterize the class C_G of all torsion abelian groups T satisfying Ext(G,T)=0 assuming the continuum hypothesis CH. Moreover, in Godel's…