lean_workbook_plus_48461

Proved

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

For real numbers $a, b, c,$ prove that \n\n

|a|+|b|+|c|+|a+b+c|\ge |a+b|+|b+c|+|c+a|

Old .

Preamble

import Mathlib.Analysis.Complex.Basic

Formal statement

theorem lean_workbook_plus_48461 (a b c : ℝ) : abs a + abs b + abs c + abs (a + b + c) ≥ abs (a + b) + abs (b + c) + abs (c + a)   :=  by sorry

Source