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arXiv 2402.01329math.LO
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AD$^+$ 蕴含 $ω_1$ 是 $Θ$-Berkeley 基数

AD$^+$ implies that $ω_1$ is a $Θ$-Berkeley cardinal

Douglas Blue, Grigor Sargsyan

AI总结:

本文在 AD$^+$ 下证明正则 Suslin 基数、$ω_1$ 及 ${\tildeδ}^1_{2n}$ 等具有不同强度的 $Θ$-Berkeley 性质,并说明 $ω_1$ 非 $Θ^+$-Berkeley 从而结果最优。

摘要:

沿用 \cite{bagaria2019large},给定基数 $κ<λ$,我们称 $κ$ 是 club $λ$-Berkeley 基数,如果对每个满足 $κ\subseteq N$ 且规模 $<λ$ 的传递集 $N$,都存在 club $C\subseteq κ$,使得对每个 $η\in C$,都有初等嵌入 $j: N\rightarrow N$ 且 crit$(j)=η$。若上述 $C\subseteq κ$ 是 $ν$-club,则称 $κ$ 是 $ν$-club $λ$-Berkeley;若 $C$ 在 $κ$ 中无界,则称 $κ$ 是 $λ$-Berkeley。我们证明在 AD$^+$ 下,(1) 每个正则 Suslin 基数都是 $ω$-club $Θ$-Berkeley(见 \rthm{main theorem}),(2) $ω_1$ 是 club $Θ$-Berkeley(见 \rthm{main theorem lr} 和 \rthm{main theorem}),以及 (3) 诸 ${\tildeδ}^1_{2n}$ 都是 $Θ$-Berkeley——特别地,$ω_2$ 是 $Θ$-Berkeley(见 \rrem{omega2})。在此过程中,我们在直接极限中把正则 Suslin 基数表示为切点基数(见 \rthm{char extenders})。该主题已在 \cite{MPSC} 和 \cite{jackson2022suslin} 中被研究,尽管视角不同。我们还证明,假设 $V=L(\mathbb{R})+{\mathrm{AD}}$,$ω_1$ 不是 $Θ^+$-Berkeley,因此标题所述结果是不可改进的(见 \rthm{lr optimal} 和 \rthm{thetareg optimal})。

英文摘要:

Following \cite{bagaria2019large}, given cardinals $κ<λ$, we say $κ$ is a club $λ$-Berkeley cardinal if for every transitive set $N$ of size $<λ$ such that $κ\subseteq N$, there is a club $C\subseteq κ$ with the property that for every $η\in C$ there is an elementary embedding $j: N\rightarrow N$ with crit$(j)=η$. We say $κ$ is $ν$-club $λ$-Berkeley if $C\subseteq κ$ as above is a $ν$-club. We say $κ$ is $λ$-Berkeley if $C$ is unbounded in $κ$. We show that under AD$^+$, (1) every regular Suslin cardinal is $ω$-club $Θ$-Berkeley (see \rthm{main theorem}), (2) $ω_1$ is club $Θ$-Berkeley (see \rthm{main theorem lr} and \rthm{main theorem}), and (3) the ${\tildeδ}^1_{2n}$'s are $Θ$-Berkeley -- in particular, $ω_2$ is $Θ$-Berkeley (see \rrem{omega2}). Along the way, we represent regular Suslin cardinals in direct limits as cutpoint cardinals (see \rthm{char extenders}). This topic has been studied in \cite{MPSC} and \cite{jackson2022suslin}, albeit from a different point of view. We also show that, assuming $V=L(\mathbb{R})+{\mathrm{AD}}$, $ω_1$ is not $Θ^+$-Berkeley, so the result stated in the title is optimal (see \rthm{lr optimal} and \rthm{thetareg optimal}).

机构、总结、中文摘要均由AI分析而来,可能存在错误,请以论文正文为准。

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