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A solution to Roitman's problem

Published 29 Apr 2014 in math.LO | (1404.7343v3)

Abstract: We answer Question~3.2 from Shelah \cite{Sh:666}: Given a maximal almost disjoint (mad) family A\mathcal A of size ℵ1\aleph_1, we construct a forcing Q(A){\mathbb Q}(\mathcal A) that has Axiom A, is <sup>ω</sup>ω{}<sup>\omega</sup> \omega-bounding, preserves selective ultrafilters, has the ℵ2\aleph_2-properness isomorphism condition (p.i.c.), and destroys the mad family A\mathcal A. We develop a new construction technique for partial orders, combining ladder systems for ω1\omega_1 with trees of normed creatures. Countable support iteration of the new kind of iterands solves Roitman's problem in the case of d=ℵ1d=\aleph_1 and also simultaneously the open question about the relative consistency of $u = \aleph_1 &lt; a$: It is consistent relative to ZFC that there is a dominating set of size ℵ1\aleph_1 and a selective ultrafilter with character ℵ1\aleph_1 and the minimal size of a mad family is ℵ2\aleph_2, like the continuum.

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