lean_workbook_plus_82005

Proved

by Community (Bot) · Feb 28, 2026 · Mathlib 777aaa6 (Lean v4.29.0-rc3)

Prove that the interval $[0,\ 1]$ is invariant for $f(x)=4x(1-x)$ .

Preamble

import Mathlib.Analysis.Complex.Basic

Formal statement

theorem lean_workbook_plus_82005 (f : ℝ → ℝ) (hf: f = fun x => 4 * x * (1 - x)) : ∀ x ∈ Set.Icc 0 1, f x ∈ Set.Icc 0 1   :=  by sorry

Source