lean_workbook_plus_13378

Proved

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

bc + ca + ab + 1 > 0 for the case when the numbers a, b, c are all $\leq 0$

Preamble

import Mathlib.Analysis.Complex.Basic

Formal statement

theorem lean_workbook_plus_13378 (a b c : ℝ) (ha : a ≤ 0) (hb : b ≤ 0) (hc : c ≤ 0) : (b * c + c * a + a * b + 1) > 0   :=  by sorry

Source