Xavier Claeys, Ralf Hiptmair and Elke Spindler. (2018). Second-Kind Boundary Integral Equations for Scattering at Composite Partly Impenetrable Objects.
            <i>Communications in Computational Physics</i>. <i>23</i> (1).
            264-295.
         doi:10.4208/cicp.OA-2016-0171