Equation Icon  ⟨ ⟩ ⟨ ⟩ ⟨ ⟩ ℋ μναβ(x,x′) ≡ ¯hμν(x)¯hαβ(x ′) − ¯hμν(x) ¯h αβ(x′) ⟨ ⟩s s s = ¯hμfν(x)¯h αfβ(x′) . (141 ) s