Equation Icon  hαβ → h′ = hαβ + Δh αβ αβ = hαβ + 𝜀£ ξ(1)gαβ + 12𝜀2(£ξ(2) + £2ξ(1))gαβ + 𝜀2£ ξ(1)h (1α)β + O(𝜀3). (21.13 )