“…As mentioned already above, the arguments introduced were developed into a methodology for establishing existence from uniqueness for classes of second kind integral equations on unbounded domains and for analyzing the convergence and stability of approximation methods in a series of papers by the first author and collaborators [15,77,23,27,70,21,26,7,8]. A particular motivation for this was the analysis of integral equation methods for problems of scattering of acoustic, elastic and electromagnetic waves by unbounded surfaces [16,24,112,22,25,70,21,113,75,8,19]. Other applications included the study of multidimensional Wiener-Hopf operators and, related to the Schrödinger operator, a study of Lippmann-Schwinger integral equations [23].…”