lean_workbook_plus_59462

Proved

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

Let $a,b$ be reals such that $(a^2+1)(b^2+1)=4$ . Prove that $(a+1)(b-1)\geq -4$

Preamble

import Mathlib.Analysis.Complex.Basic

Formal statement

theorem lean_workbook_plus_59462 (a b : ℝ) (hab : (a^2 + 1) * (b^2 + 1) = 4) : (a + 1) * (b - 1) ≥ -4   :=  by sorry

Source