\[U\left(a,z\right)=\pm ie^{\pm i\pi a}U\left(a,-z\right)+\frac{\sqrt{2\pi}}{%
\Gamma\left(\tfrac{1}{2}+a\right)}e^{\pm i\pi(\frac{1}{2}a-\frac{1}{4})}U\left%
(-a,\pm iz\right).\]