In mathematics, Schur's inequality, named after Issai Schur, establishes that for all non-negative real numbers x, y, z, and t>0, ∑ c y c x t = x t + y t + z t ≥ 0 {\displaystyle \sum _{cyc}x^{t}=x^{t}+y^{t}+z^{t}\geq 0} with equality if and only if x = y = z or two of them are equal and the other is zero. Wikipedia