Equation Icon  αβ ′ αβ ′ H γ′δ′(x, x ) = V γ′δ′(x,x ), (16.36 ) αβ ′ 1 αβ ′ 1 αβ ′ G S γ′δ′(x, x ) = 2U γ′δ′(x,x )δ(σ) − 2V γ′δ′(x,x )𝜃(σ), (16.37 ) 1 [ ] [ 1 ] G Rαβγ′δ′(x, x′) = -U αβγ′δ′(x,x′) δ+(σ) − δ− (σ ) + V αβγ′δ′(x,x′) 𝜃+(− σ) +-𝜃(σ ) . (16.38 2 2