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.
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The upper attic
The middle attic
The lower attic
The parlour
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Cantor's Attic (original site)
Joel David Hamkins blog post about the Attic
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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 $N$.
Elements of $OD$ are all definable from a finite collection of ordinals.
Generic HOD (gHOD) is the intersection of HODs of all set-generic extensions of $V$. (Fuchs et al., 2015)
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