Hℓ+⁡(η,ρ)=ⅈ⁢ⅇ-π⁢η⁢ρℓ+1(2⁢ℓ+1)!⁢Cℓ⁡(η)⁢∫-1-ⅈ⁢∞ⅇ-ⅈ⁢ρ⁢t⁢(1-t)ℓ-ⅈ⁢η⁢(1+t)ℓ+ⅈ⁢η⁢ⅆ⁡t.