Abstract
Under various set-theoretic hypotheses we construct families of maximal possible size of almost free abelian groups which are pairwise almost disjoint, i.e. there is no non-free subgroup embeddable in two of them. We show that quotient-equivalent groups cannot be almost disjoint, but we show how to construct maximal size families of quotient-equivalent groups of cardinality ℵ1, which are mutually non-embeddable.
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Dedicated to the memory of Abraham Robinson on the tenth anniversary of this death
First and third authors acknowledge assistance from the US-Israel Binational Science Foundation, Grant No. 1110. First author partially supported by NSF Grant No. MCS-8003691. Second author acknowledges support from the National Science and Engineering Research Council of Canada, Grant No. U0075
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Eklof, P.C., Mekler, A.H. & Shelah, S. Almost disjoint abelian groups. Israel J. Math. 49, 34–54 (1984). https://doi.org/10.1007/BF02760645
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DOI: https://doi.org/10.1007/BF02760645