lean_workbook_plus_56852

Proved

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

Given $f: \mathbb{R}\rightarrow \mathbb{R}$ , prove that if $f(f(x)) = x$ for all $x \in \mathbb{R}$ , then $f$ is bijective.

Preamble

import Mathlib.Analysis.Complex.Basic

Formal statement

theorem lean_workbook_plus_56852 (f : ℝ → ℝ) (hf: f ∘ f = id) : Function.Bijective f   :=  by sorry

Source