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FORCING AXIOMS AND THE DEFINABILITY OF THE NONSTATIONARY IDEAL ON THE FIRST UNCOUNTABLE

Part of: Set theory

Published online by Cambridge University Press:  19 June 2023

STEFAN HOFFELNER Open the ORCID record for STEFAN HOFFELNER [Opens in a new window] ,
PAUL LARSON ,
RALF SCHINDLER  and
LIUZHEN WU
STEFAN HOFFELNER*
Affiliation:
INSTIUT FÜR MATHEMATISCHE LOGIK UND GRUNDLAGENFORSCHUNG WWU MÜNSTER, EINSTEINSTRAßE 62 48149 MÜNSTER, GERMANY
PAUL LARSON
Affiliation:
DEPARTMENT OF MATHEMATICS, MIAMI UNIVERSITY 301 S. PATTERSON AVENUE, 123 BACHELOR HALL OXFORD, OH 45056, USA E-mail: larsonpb@miamioh.edu URL: https://www.users.miamioh.edu/larsonpb/
RALF SCHINDLER
Affiliation:
INSTITUT FÜR MATHEMATISCHE LOGIK UND GRUNDLAGENFORSCHUNG UNIVERSITÄT MÜNSTER EINSTEINSTRAßE 62 48149 MÜNSTER, GERMANY E-mail: rds@uni-muenster.de URL: https://ivv5hpp.uni-muenster.de/u/rds/
LIUZHEN WU
Affiliation:
INSTITUTE OF MATHEMATICS, CHINESE ACADEMY OF SCIENCES NO. 55, EAST ZHONG GUAN CUN ROAD BEIJING 100190, CHINA E-mail: lzwu@math.ac.cn URL: http://people.ucas.ac.cn/lzwu
*
E-mail: stefan.hoffelner@gmx.at
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Abstract

We show that under $\mathsf {BMM}$ and “there exists a Woodin cardinal,$"$ the nonstationary ideal on $\omega _1$ cannot be defined by a $\Pi _1$ formula with parameter $A \subset \omega _1$. We show that the same conclusion holds under the assumption of Woodin’s $(\ast )$-axiom. We further show that there are universes where $\mathsf {BPFA}$ holds and $\text {NS}_{\omega _1}$ is $\Pi _1(\{\omega _1\})$-definable. Lastly we show that if the canonical inner model with one Woodin cardinal $M_1$ exists, there is a generic extension of $M_1$ in which $\text {NS}_{\omega _1}$ is saturated and $\Pi _1(\{ \omega _1\} )$-definable, and $\mathsf {MA_{\omega _1}}$ holds.

Keywords

nonstationary idealdefinabilityforcing axioms

MSC classification

Primary: 03E35: Consistency and independence results
Secondary: 03E45: Inner models, including constructibility, ordinal definability, and core models 03E55: Large cardinals 03E57: Generic absoluteness and forcing axioms
Type
Article
Information
The Journal of Symbolic Logic , First View , pp. 1 - 18
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Copyright
© The Author(s), 2023. Published by Cambridge University Press on behalf of The Association for Symbolic Logic

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