Bolzano–Weierstrass theorem
Closed
Theorem & proof
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bolzano_weierstrass.lean
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import Mathlib theorem bolzano_weierstrass {s : Set ℝ} (h : Bornology.IsBounded s) (hs : s.Infinite) : ∃ x, AccPt x (Filter.principal s) := by have hK_closed : IsClosed (closure s) := isClosed_closure have hK_bounded : Bornology.IsBounded (closure s) := Metric.isBounded_closure_of_isBounded h have hK_compact : IsCompact (closure s) := Metric.isCompact_iff_isClosed_bounded.2 ⟨hK_closed, hK_bounded⟩ rcases hs.exists_accPt_of_subset_isCompact hK_compact subset_closure with ⟨x, _, hx⟩ exact ⟨x, hx⟩
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