\[K_{\nu}\left(\nu z\right)=\left(\frac{\pi}{2\nu}\right)^{\frac{1}{2}}\frac{e^{%
-\nu\eta}}{(1+z^{2})^{\frac{1}{4}}}\*\left(\sum_{k=0}^{\ell-1}(-1)^{k}\frac{U_%
{k}(p)}{\nu^{k}}+O\left(\frac{1}{z^{\ell}}\right)\right),\]