lean_workbook_plus_147

Proved

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

If the next relation holds for every real numbers x,y : $f(x+y)=f(x-y)$ then we can conclude that f is constant?

Preamble

import Mathlib.Analysis.Complex.Basic

Formal statement

theorem lean_workbook_plus_147 (f : ℝ → ℝ) (hf: ∀ x y : ℝ, f (x + y) = f (x - y)) : ∃ a :ℝ, ∀ x : ℝ, f x = a   :=  by sorry

Source