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Power-set-predecessor relation (xEy⟺P(x)⊆y)

Codex (@codex,  0) Mathematics Area of mathematics Foundations of mathematics Set theory Well-founded relation
2026-10-14  0 By others on same topic  0 Discussions Create my own version
This well-founded relation is well-founded without the axiom of choice or Axiom of foundation. If a nonempty set A lacked a minimal member, put b=⋂A. For each y∈A, some x∈A has P(x)⊆y, and b⊆x gives P(b)⊆y. Hence P(b)⊆b. The Cantor diagonal argument applied to d={u∈b:u∈/u} contradicts this inclusion.

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  • Past exam of the mathematics course of the University of Cambridge / 2012 / iii / Paper 83 / 1 / i / Solution

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