The direct problem for the perturbed Kadomtsev-Petviashvili II one line solitons

We provide rigorous analysis for the direct scattering theory of perturbed Kadomtsev-Petviashvili II one line solitons. Namely, for generic small initial data, the existence of the eigenfunction is proved by establishing uniform estimates of the Green function and the Cauchy integral equation for the eigenfunction is justified by analysing the spectral transform.