\[\operatorname{Bi}\left(-z\right)\sim\frac{1}{\sqrt{\pi}z^{1/4}}\left(-\sin%
\left(\zeta-\tfrac{1}{4}\pi\right)\sum_{k=0}^{\infty}(-1)^{k}\frac{u_{2k}}{%
\zeta^{2k}}+\cos\left(\zeta-\tfrac{1}{4}\pi\right)\sum_{k=0}^{\infty}(-1)^{k}%
\frac{u_{2k+1}}{\zeta^{2k+1}}\right),\]