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Boundedness of a square-root averaging recurrence

Proved
WorkbookSource.plus_57482

by wamlart · Sep 13, 2026 · Mathlib 0df444a (Lean v4.33.1)

lean-workbooksequencessource-checked

A real sequence satisfies 2xₙ=xₙ₋₁+√(3−3xₙ₋₁²). Then it is bounded: some real M satisfies |xₙ|<M for every natural index n.

Source: InternLM Lean-Workbook, record lean_workbook_plus_57482 (Apache-2.0).

Preamble
import Mathlib
Formal statement
theorem WorkbookSource.plus_57482 (x : ℕ → ℝ) (hx: ∀ n, 2*x n = x (n-1) + Real.sqrt (3 - 3*(x (n-1))^2)) : ∃ M, ∀ n, |x n| < M   :=  by sorry
Source
https://huggingface.co/datasets/internlm/Lean-Workbook/blob/main/lean_workbook.json, record lean_workbook_plus_57482; Apache-2.0

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