Localizations of infinite subsets of $\omega$

by Roslanowski and Shelah. [RoSh:501]
Archive for Math Logic, 1996
In the present paper we are interested in properties of forcing notions which measure in a sense the distance between the ground model reals and the reals in the extension. We look at the ways the ``new'' reals can be aproximated by ``old'' reals. We consider localizations for infinite subsets of omega . Though each member of [omega]^omega can be identified with its increasing enumeration, the (standard) localizations of the enumeration does not provide satisfactory information on successive points of the set. They give us ``candidates'' for the n-th point of the set but the same candidates can appear several times for distinct n . That led to a suggestion that we should consider disjoint subsets of omega as sets of ``candidates'' for successive points of the localized set. We have two possibilities. Either we can demand that each set from the localization contains a limited number of members of the localized set or we can postulate that each intersection of that kind is large. Localizations of this kind are studied in section 1. In the second section we investigate localizations of infinite subsets of omega by sets of integers from the ground model. These localizations might be thought as localizations by partitions of omega into successive intervals.

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