huge cardinal

In mathematics, a cardinal number \kappa is called huge if there exists an elementary embedding j : V \to M from V into a transitive inner model M with critical point \kappa and

:{}^{j(\kappa)}M \subset M.

Here, {}^\alpha M is the class of all sequences of length \alpha whose elements are in M.

Huge cardinals were introduced by {{harvs|txt|authorlink=Kenneth Kunen|first=Kenneth |last=Kunen|year=1978}}.

Variants

In what follows, j^n refers to the n-th iterate of the elementary embedding j, that is, j composed with itself n times, for a finite ordinal n. Also, {}^{<\alpha}M is the class of all sequences of length less than \alpha whose elements are in M. Notice that for the "super" versions, \gamma should be less than j(\kappa), not {j^n(\kappa)}.

κ is almost n-huge if and only if there is j : V \to M with critical point \kappa and

:{}^{

κ is super almost n-huge if and only if for every ordinal γ there is j : V \to M with critical point \kappa, \gamma< j(\kappa), and

:{}^{

κ is n-huge if and only if there is j : V \to M with critical point \kappa and

:{}^{j^n(\kappa)}M \subset M.

κ is super n-huge if and only if for every ordinal \gamma there is j : V \to M with critical point \kappa, \gamma< j(\kappa), and

:{}^{j^n(\kappa)}M \subset M.

Notice that 0-huge is the same as measurable cardinal; and 1-huge is the same as huge. A cardinal satisfying one of the rank into rank axioms is n-huge for all finite n.

The existence of an almost huge cardinal implies that Vopěnka's principle is consistent; more precisely any almost huge cardinal is also a Vopěnka cardinal.

Kanamori, Reinhardt, and Solovay defined seven large cardinal properties between extendibility and hugeness in strength, named \mathbf A_2(\kappa) through \mathbf A_7(\kappa), and a property \mathbf A_6^\ast(\kappa).A. Kanamori, W. N. Reinhardt, R. Solovay, "[https://math.bu.edu/people/aki/d.pdf Strong Axioms of Infinity and Elementary Embeddings]", pp.110--111. Annals of Mathematical Logic vol. 13 (1978). The additional property \mathbf A_1(\kappa) is equivalent to "\kappa is huge", and \mathbf A_3(\kappa) is equivalent to "\kappa is \lambda-supercompact for all \lambda". Corazza introduced the property A_{3.5}, lying strictly between A_3 and A_4.P. Corazza, "[http://matwbn.icm.edu.pl/ksiazki/fm/fm152/fm15225.pdf A new large cardinal and Laver sequences for extendibles]", Fundamenta Mathematicae vol. 152 (1997).

Consistency strength

The cardinals are arranged in order of increasing consistency strength as follows:

  • almost n-huge
  • super almost n-huge
  • n-huge
  • super n-huge
  • almost n+1-huge

The consistency of a huge cardinal implies the consistency of a supercompact cardinal, nevertheless, the least huge cardinal is smaller than the least supercompact cardinal (assuming both exist).

ω-huge cardinals

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One can try defining an \omega-huge cardinal \kappa as one such that an elementary embedding j : V \to M from V into a transitive inner model M with critical point \kappa and {}^\lambda M\subseteq M, where \lambda is the supremum of j^n(\kappa) for positive integers n. However Kunen's inconsistency theorem shows that such cardinals are inconsistent in ZFC, though it is still open whether they are consistent in ZF. Instead an \omega-huge cardinal \kappa is defined as the critical point of an elementary embedding from some rank V_{\lambda+1} to itself. This is closely related to the rank-into-rank axiom I1.

See also

References

{{Reflist}}

{{refbegin}}

  • {{Citation|last=Kanamori|first=Akihiro|authorlink=Akihiro Kanamori|year=2003|publisher=Springer|title=The Higher Infinite : Large Cardinals in Set Theory from Their Beginnings|title-link= The Higher Infinite |edition=2nd|isbn=3-540-00384-3}}.
  • {{Citation | last=Kunen | first=Kenneth | authorlink=Kenneth Kunen | title=Saturated ideals | doi=10.2307/2271949 | jstor=2271949 | mr=495118 | year=1978 | journal=The Journal of Symbolic Logic | issn=0022-4812 | volume=43 | issue=1 | pages=65–76| s2cid=13379542 }}.
  • {{Citation|last=Maddy|first=Penelope|authorlink=Penelope Maddy|journal=The Journal of Symbolic Logic|title=Believing the Axioms. II|year=1988|volume=53|issue=3|pages=736-764 (esp. 754-756)|doi=10.2307/2274569|jstor=2274569|s2cid=16544090 }}. A copy of parts I and II of this article with corrections is available at the [http://faculty.sites.uci.edu/pjmaddy/bibliography/ author's web page].

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Category:Large cardinals