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IDEAL PROJECTIONS AND FORCING PROJECTIONS
Published online by Cambridge University Press: 12 December 2014
Abstract
It is well known that saturation of ideals is closely related to the “antichain-catching” phenomenon from Foreman–Magidor–Shelah [10]. We consider several antichain-catching properties that are weaker than saturation, and prove:
(1) If ${\cal I}$ is a normal ideal on $\omega _2 $ which satisfies stationary antichain catching, then there is an inner model with a Woodin cardinal;
(2) For any $n \in \omega $, it is consistent relative to large cardinals that there is a normal ideal ${\cal I}$ on $\omega _n $ which satisfies projective antichain catching, yet ${\cal I}$ is not saturated (or even strong). This provides a negative answer to Open Question number 13 from Foreman’s chapter in the Handbook of Set Theory ([7]).
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