Equation Icon  ℐ ( δL + δx) ℐdark(δx∕ λ0) = -0- 1 − cos 4π---0----- ≃ ( ) 2 λ(0 ) 2 δL0δx δx2 δL20 δx δx2 δL20 8π ℐ0 -λ2---+ 𝒪 λ2-,-λ2- = const. × 4π λ-+ 𝒪 -λ2-,-λ2- . (9 ) 0 0 0 0 0 0