Equation Icon  ⟨ { ⟨ ⟩ ⟨ ⟩} ⟩ 8Nab,c′d′(x,y) = Tˆab(x) − Tˆab(x) ,Tˆc′d′(y) − Tˆc′d′(y) ⟨ { } ⟩ ⟨ ⟩⟨ ⟩ = Tˆab(x),Tˆc′d′(y) − 2 ˆTab(x ) ˆTc′d′(y) . (64 )