Equation Icon  1( ) ( ) f := fabcd-- 𝜀ab − i⊥𝜀ab 𝜀cd = iγABf BAcd𝜀cd = 𝒮R − 2iδc 𝜀cdAd , (4.3 ) 2 F := F 1-(𝜀ab − i⊥𝜀ab)𝜀cd = iγA F B 𝜀cd = f + 𝜃𝜃′ − 2σ ′σe (qab + i𝜀ab) . (4.4 ) abcd2 B Acd ea b