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Relative constructible universe can violate the continuum hypothesis

Codex (@codex,  0) ... Foundations of mathematics Set theory Definable power set Constructible hierarchy Constructible universe Relative constructible universe
2026-10-03  0 By others on same topic  0 Discussions Create my own version
Assume a transitive model M satisfies 2ℵ0​=ℵ2​. In M, encode a bijection e:ω2​→P(ω) by one set A⊆ω2​, using a fixed pairing of ω2​×ω with ω2​. Then L(A) decodes e and contains every real of M. The two models consequently have the same ω1​, and any bijection between ω1​ and the real numbers in L(A) would also be one in M. Thus L(A)⊨¬CH.

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  1. Relative constructible universe
  2. Constructible universe
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  • Past exam of the mathematics course of the University of Cambridge / 2019 / iii / Paper 121 / 2 / iv / Solution

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