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Strongs-Sequences and Variations on Martin's Axiom

Published online by Cambridge University Press:  20 November 2018

Juris Steprāns*
Affiliation:
York University, Downsview, Ontario
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As part of their study of βωω and βω1ω1, A. Szymanski and H. X. Zhou [3] were able to exploit the following difference between ω, and ω: ω1, contains uncountably many disjoint sets whereas any uncountable family of subsets of ω is, at best, almost disjoint. To translate this distinction between ω1, and ω to a possible distinction between βω1ω1, and βωω they used the fact that if a pairwise disjoint family of sets and a subset of each member of is chosen then it is trivial to find a single set whose intersection with each member is the chosen set. However, they noticed, it is not clear that the same is true if is only a pairwise almost disjoint family even if we only require equality except on a finite set. But any homeomorphism from βω1ω1 to βωω would have to carry a disjoint family of subsets of ω1, to an almost disjoint family of subsets of ω with this property. This observation should motivate the following definition.

Type
Research Article
Copyright
Copyright © Canadian Mathematical Society 1985

References

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3. Szymanski, A. and Zhou, H. X., preprint.Google Scholar
4. Tall, F., Some applications of a generalized Martin's Axiom, to appear in Trans. A.M.S.Google Scholar
5. Weiss, W., Versions of Martin's Axiom, to appear in The Handbook of Set Theoretic Topology.Google Scholar