cantors-attic

Climb into Cantor’s Attic, where you will find infinities large and small. We aim to provide a comprehensive resource of information about all notions of mathematical infinity.

View the Project on GitHub neugierde/cantors-attic

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The upper attic
The middle attic
The lower attic
The parlour
The playroom
The library
The cellar

Sources
Cantor's Attic (original site)
Joel David Hamkins blog post about the Attic
Latest working snapshot at the wayback machine

HOD

HOD denotes the class of Hereditarily Ordinal Definable sets. It is a definable canonical inner model of ZFC.

Although it is definable, this definition is not absolute for transitive inner models of ZF, i.e. given two models $M$ and $N$ of $ZF$, $HOD$ as computed in $M$ may differ from $HOD$ as computed in $N$.

Ordinal Definable Sets

Elements of $OD$ are all definable from a finite collection of ordinals.

Relativizations

gHOD

Generic HOD (gHOD) is the intersection of HODs of all set-generic extensions of $V$. (Fuchs et al., 2015)

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References

  1. Fuchs, G., Hamkins, J. D., & Reitz, J. (2015). Set-theoretic geology. Annals of Pure and Applied Logic, 166(4), 464–501. https://doi.org/http://web.archive.org/web/20191116153209/https://doi.org/10.1016/j.apal.2014.11.004
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