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On a topological construction of Juhasz and Shelah

Published online by Cambridge University Press:  12 March 2014

Dan Velleman*
Affiliation:
Department of Mathematics, Amherst College, Amherst, Massachusetts 01002, E-mail: [email protected]

Extract

In [2], Juhasz and Shelah use a forcing argument to show that it is consistent with GCH that there is a 0-dimensional T2 topological space X of cardinality 3 such that every partition of the triples of X into countably many pieces has a nondiscrete (in the topology) homogeneous set. In this paper we will show how to construct such a space using a simplified (ω2, 1)-morass with certain additional structure added to it. The additional structure will be a slight strengthening of a built-in ◊ sequence, analogous to the strengthening of ordinary ◊k to ◊S for a stationary set Sk.

Suppose 〈〈θα ∝ ≤ ω2〉, 〈∝βα < βω2〉〉 is a neat simplified (ω2, 1)-morass (see [3]). Let be a language with countably many symbols of all types, and suppose that for each α < ω2, α is an -structure with universe θα. The sequence 〈αα < ω2 is called a built-insequence for the morass if for every -structure with universe ω3 there is some α < ω2 and some f ∈αω2 such that f(α) ≺ , where f(α) is the -structure isomorphic to α under the isomorphism f. We can strengthen this slightly by assuming that α is only defined for αS, for some stationary set Sω2. We will then say that is a built-insequence on levels in S if for every -structure with universe ω3 there is some αS and some fαω2 such that f(α) ≺ .

Type
Research Article
Copyright
Copyright © Association for Symbolic Logic 1992

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References

REFERENCES

[1]Donder, H.-D., Another look at gap-1 morasses, Recursion theory, Proceedings of Symposia in Pure Mathematics, vol. 42, American Mathematical Society, Providence, Rhode Island, 1985, pp. 223236.CrossRefGoogle Scholar
[2]Juhasz, I. and Shelah, S., On partitioning the triples of a topological space, Proceedings of the 1989 Oxford topology conference (to appear).Google Scholar
[3]Velleman, D., Simplified morasses, this Journal, vol. 49 (1984), pp. 257271.Google Scholar
[4]Velleman, D., Simplified morasses with linear limits, this Journal, vol. 49 (1984), pp. 10011021.Google Scholar