G3⁡(α,α′;x,y)=∑m,n=0∞Γ⁡(α+2⁢n-m)⁢Γ⁡(α′+2⁢m-n)Γ⁡(α)⁢Γ⁡(α′)⁢xm⁢ynm!⁢n!,