U⁡(a,b,z)=z-a2⁢π⁢ⅈ⁢∫-ⅈ⁢∞ⅈ⁢∞Γ⁡(a+t)⁢Γ⁡(1+a-b+t)⁢Γ⁡(-t)Γ⁡(a)⁢Γ⁡(1+a-b)⁢z-t⁢ⅆ⁡t,