Scattering and Inverse Scattering for Steplike Potentials in the Schroedinger Equation Amy CohenThomas Kappeler Indiana University Mathematics Journal 1985 text pdf 10.1512/iumj.1985.34.34008 10.1512/iumj.1985.34.34008 en Indiana Univ. Math. J. 34 (1985) 127 - 180 state-of-the-art mathematics http://iumj.org/access/