Equation Icon  ⟨ ⟩ ⟨ ⟩ 𝒢μναβ(x,x′) ≡ G (1)μν(x )G (1)α β(x ′) s − ⟨G(1)μν(x)⟩s G (1)αβ(x′) s ⟨ (1)μν (1)αβ ⟩ = G f (x)G f (x′) . (127 ) s