The resurrection axioms are forcing axioms introduced recently by Hamkins and Johnstone, developing on ideas of Chalons and Velickovi\'c. We introduce a stronger form of resurrection axioms (the \emph{iterated} resurrection axioms RAα(Γ) for a class of forcings Γ and a given ordinal α), and show that RAω(Γ) implies generic absoluteness for the first-order theory of Hγ+ with respect to forcings in Γ preserving the axiom, where γ=γΓ is a cardinal which depends on Γ (γΓ=ω1 if Γ is any among the classes of countably closed, proper, semiproper, stationary set preserving forcings). We also prove that the consistency strength of these axioms is below that of a Mahlo cardinal for most forcing classes, and below that of a stationary limit of supercompact cardinals for the class of stationary set preserving posets. Moreover we outline that simultaneous generic absoluteness for Hγ+0 with respect to Γ0 and for Hγ+1 with respect to Γ1 with γ0=γΓ0≠γΓ1=γ1 is in principle possible, and we present several natural models of the Morse Kelley set theory where this phenomenon occurs (even for all Hγ simultaneously). Finally, we compare the iterated resurrection axioms (and the generic absoluteness results we can draw from them) with a variety of other forcing axioms, and also with the generic absoluteness results by Woodin and the second author.
Absoluteness via resurrection
AUDRITO, GIORGIO;VIALE, Matteo
2017-01-01
Abstract
The resurrection axioms are forcing axioms introduced recently by Hamkins and Johnstone, developing on ideas of Chalons and Velickovi\'c. We introduce a stronger form of resurrection axioms (the \emph{iterated} resurrection axioms RAα(Γ) for a class of forcings Γ and a given ordinal α), and show that RAω(Γ) implies generic absoluteness for the first-order theory of Hγ+ with respect to forcings in Γ preserving the axiom, where γ=γΓ is a cardinal which depends on Γ (γΓ=ω1 if Γ is any among the classes of countably closed, proper, semiproper, stationary set preserving forcings). We also prove that the consistency strength of these axioms is below that of a Mahlo cardinal for most forcing classes, and below that of a stationary limit of supercompact cardinals for the class of stationary set preserving posets. Moreover we outline that simultaneous generic absoluteness for Hγ+0 with respect to Γ0 and for Hγ+1 with respect to Γ1 with γ0=γΓ0≠γΓ1=γ1 is in principle possible, and we present several natural models of the Morse Kelley set theory where this phenomenon occurs (even for all Hγ simultaneously). Finally, we compare the iterated resurrection axioms (and the generic absoluteness results we can draw from them) with a variety of other forcing axioms, and also with the generic absoluteness results by Woodin and the second author.File | Dimensione | Formato | |
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