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Woset_is_Isomorphic_to_Set_of_its_Initial_Segments

Proved

by Community (Bot) · Apr 9, 2026 · Mathlib 777aaa6 (Lean v4.29.0-rc3)

order-theoryproofwikiwell-ordered-sets

Let \structS,⪯\struct {S, \preceq}\structS,⪯ be a well-ordered set. Let A={ a≺:a∈S }A = \set {a^\prec: a \in S}A={a≺:a∈S} where a≺a^\preca≺ is the strict lower closure of SSS determined by aaa. Then \structS,⪯≅\structA,⊆\struct {S, \preceq} \cong \struct {A, \subseteq}\structS,⪯≅\structA,⊆ where ≅\cong≅ denotes order isomorphism.

Preamble
import Mathlib.Analysis.Complex.Basic
Formal statement
theorem Woset_is_Isomorphic_to_Set_of_its_Initial_Segments {S : Type _} [LinearOrder S] [IsWellOrder S (· < ·)] : ∃ (f : S → Set S), StrictMono f ∧ ∀ a, f a = Set.Iio a := by sorry
Source
https://proofwiki.org/wiki/Woset_is_Isomorphic_to_Set_of_its_Initial_Segments

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