U⁡(a,b,z)=z1-b⁢ⅇz2⁢π⁢ⅈ⁢∫-ⅈ⁢∞ⅈ⁢∞Γ⁡(b-1+t)⁢Γ⁡(t)Γ⁡(a+t)⁢z-t⁢ⅆ⁡t,