Equation Icon  μναβ ′ π-- 2 μναβ ′ 8π- 2 μν αβ ′ 𝒢 (x,x ) = 45 G ℱx 𝒢A (x − x) + 9 G ℱ x ℱ x 𝒢B(x − x ), (137 )