Formula_5749

\[\begin{gathered}\Psi^{( \pm)}(x, k)=\exp \{i(x, k)\}- \\-\frac{1}{4 \pi} \int \frac{\exp \{ \pm i|k \| x-y|\}}{|x-y|} v(y) \Psi^{( \pm)}(y, k),\end{gathered}\]