Answer by Dmytro Taranovsky for Can two versions of...
Every ordinal $α$ that is the least ordinal satisfying a given $Σ^1_1$ property (about $α$, equivalently, about $L_α$) is a Gandy ordinal, so $\mathsf{Def}(L_α)=\mathsf{Ad}(L_α)$. This includes the...
View ArticleCan two versions of $\omega_1^{CK}(\mathsf{Ord})$ ever coincide?
The goal of this question is to fill in the gap in this old answer of mine.For a transitive set $M$, thought of as an $\{\in\}$-structure, we define the following ordinals (this is not the notation...
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