• Corpus ID: 173991189

The definability of the extender sequence $\mathbb{E}$ from $\mathbb{E}{\upharpoonright}\aleph_1$ in $L[\mathbb{E}]$.

@article{Schlutzenberg2019TheDO,
  title={The definability of the extender sequence \$\mathbb\{E\}\$ from \$\mathbb\{E\}\{\upharpoonright\}\aleph\_1\$ in \$L[\mathbb\{E\}]\$.},
  author={Farmer Schlutzenberg},
  journal={arXiv: Logic},
  year={2019}
}

• F. Schlutzenberg
• Published 1 June 2019
• Mathematics
• arXiv: Logic

Let $M$ be an iterable fine structural mouse.
We prove that if $E\in M$ and $M\models$``$E$ is a countably complete short extender whose support is a cardinal $\theta$ and $\mathcal{H}_\theta\subseteq\mathrm{Ult}(V,E)$'' then $E$ is in the extender sequence $\mathbb{E}^M$ of $M$. We also prove other related facts, and use them to establish that if $\kappa$ is an uncountable cardinal of $M$ and $(\kappa^+)^M$ exists in $M$ then $(\mathcal{H}_{\kappa^+})^M$ satisfies the Axiom of Global Choice.
We then prove that if $M$ satisfies the Power Set Axiom then $\mathbb{E}^M$ is definable over the universe of $M$ from the parameter $X=\mathbb{E}^M{\upharpoonright}\aleph_1^M$, and therefore $M$ satisfies ``Every set is $\mathrm{OD}_X$''. We also prove various local versions of this fact in which $M$ has a largest cardinal, and a version for generic extensions of $M$.
As a consequence, for example, the minimal proper class mouse with a Woodin limit of Woodin cardinals models ``$V=\mathrm{HOD}$''. This adapts to many other similar examples.
We also describe a simplified approach to Mitchell-Steel fine structure, which does away with the parameters $u_n$.