TY - JOUR
T1 - Kulikov's problem on universal torsion-free abelian groups
AU - Shelah, Saharon
AU - Strüngmann, Lutz
PY - 2003/6
Y1 - 2003/6
N2 - Let T be an abelian group and λ an uncountable regular cardinal. The question of whether there is a λ-universal group U among all torsion-free abelian groups G of cardinality less than or equal to A satisfying Ext(G, T) = 0 is considered. U is said to be λ-universal for T if, whenever a torsion-free abelian group G of cardinality at most λ, satisfies Ext(G, T) = 0, there is an embedding of G into U. For large classes of abelian groups T and cardinals λ, it is shown that the answer is consistently no, that is to say, there is a model of ZFC in which, for pairs T and λ, there is no universal group. In particular, for T torsion, this solves a problem by Kulikov.
AB - Let T be an abelian group and λ an uncountable regular cardinal. The question of whether there is a λ-universal group U among all torsion-free abelian groups G of cardinality less than or equal to A satisfying Ext(G, T) = 0 is considered. U is said to be λ-universal for T if, whenever a torsion-free abelian group G of cardinality at most λ, satisfies Ext(G, T) = 0, there is an embedding of G into U. For large classes of abelian groups T and cardinals λ, it is shown that the answer is consistently no, that is to say, there is a model of ZFC in which, for pairs T and λ, there is no universal group. In particular, for T torsion, this solves a problem by Kulikov.
UR - http://www.scopus.com/inward/record.url?scp=0038577062&partnerID=8YFLogxK
U2 - 10.1112/S0024610703004216
DO - 10.1112/S0024610703004216
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AN - SCOPUS:0038577062
SN - 0024-6107
VL - 67
SP - 626
EP - 642
JO - Journal of the London Mathematical Society
JF - Journal of the London Mathematical Society
IS - 3
ER -