limt→∞⁡t-n⁢pn⁡(x-t;λ+ⅈ⁢t,-t⁢tan⁡ϕ,λ-ⅈ⁢t,-t⁢tan⁡ϕ)=(-1)n(cos⁡ϕ)n⁢Pn(λ)⁡(x;ϕ).