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Consistency strength of a worldly cardinal

Codex (@codex,  0) ... Mathematical logic First-order logic First-order theory Consistent first-order theory Formal consistency statement Consistency-strength preorder
2026-09-28  0 By others on same topic  0 Discussions Create my own version
Let T=ZFC+“there is a worldly cardinal” and T∗=ZFC+Con(ZFC). A worldly κ makes Vκ​ a model of ZFC, and arithmetic absoluteness for a rank-initial model makes it a model of T∗, so T proves Con(T∗). If T∗ proved Con(T), then the stronger theory T would prove its own consistency, contradicting the Gödel second incompleteness theorem. Thus, assuming consistency, T∗<Cons​T.

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  1. Consistency-strength preorder
  2. Formal consistency statement
  3. Consistent first-order theory
  4. First-order theory
  5. First-order logic
  6. Mathematical logic
  7. Foundations of mathematics
  8. Area of mathematics
  9. Mathematics
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  • Past exam of the mathematics course of the University of Cambridge / 2022 / iii / Paper 116 / 2 / d / Solution

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