lean_workbook_plus_41089

Proved

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

For $z = x + iy$ , if $|z - 1| < |z + 3|$ , then $x > -1$ .

Preamble

import Mathlib.Analysis.Complex.Basic

Formal statement

theorem lean_workbook_plus_41089 (z : ℂ) (h : ‖z - 1‖ < ‖z + 3‖) : z.re > -1   :=  by sorry

Source