lean_workbook_plus_8312

import Mathlib.Analysis.Complex.Basic

theorem lean_workbook_plus_8312 (x y z a b c : ℝ) : a = y + z ∧ b = z + x ∧ c = x + y → x = (b + c - a) / 2 ∧ y = (a + c - b) / 2 ∧ z = (a + b - c) / 2   :=  by sorry