Gℓ⁡(η,ρ)∼ρ-ℓ(ℓ+12)⁢λℓ⁡(η)⁢Cℓ⁡(η)⁢∑k=2⁢ℓ+1∞(-1)k⁢bk⁢tk/2⁢Kk⁡(2⁢t),