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New facts
Authors:Sy D Friedman
Institution:Department of Mathematics Massachusetts Institute of Technology, Cambridge, Massachusetts 02139
Abstract:We use ``iterated square sequences' to show that there is an $L$-definable partition $n:L{\text-}Singulars \to \omega$ such that if $M$ is an inner model not containing $0^\#$:
(a)
For some $k, M \models \{\alpha|n(\alpha)\leq k\}$ is stationary.
(b)
For each $k$ there is a generic extension of $M$ in which $0^\#$ does not exist and $\{\alpha|n(\alpha)\leq k\}$ is non-stationary.
This result is then applied to show that if $M$ is an inner model without $0^\#$, then some $\Sigma^1_3$ sentence not true in $M$ can be forced over $M$.

Keywords:Class forcing  absoluteness  partitions
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