$\Delta _1$-Definability of the non-stationary ideal at successor cardinals
Volume 229 / 2015
Fundamenta Mathematicae 229 (2015), 231-254
MSC: Primary 03E35, 03E20; Secondary 03E45.
DOI: 10.4064/fm229-3-2
Abstract
Assuming $V=L$, for every successor cardinal $\kappa $ we construct a GCH and cardinal preserving forcing poset $\mathbb {P}\in L$ such that in $L^{\mathbb {P}}$ the ideal of all non-stationary subsets of $\kappa $ is $\Delta _1$-definable over $H(\kappa ^{+})$.
