lean_workbook_plus_27888

Proved

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

Prove: $|a|+|b|+|c|+|a+b+c|\geq |a+b|+|a+c|+|b+c|$

Preamble

import Mathlib.Analysis.Complex.Basic

Formal statement

theorem lean_workbook_plus_27888 (a b c : ℝ) : abs a + abs b + abs c + abs (a + b + c) ≥ abs (a + b) + abs (a + c) + abs (b + c)   :=  by sorry

Source