@incollection{JEDP_1987____A11_0,
     author = {Petkov, Vesselin M. and Stoyanov, Luchezar N.},
     title = {Singularities of the scattering kernel for non convex obstacles},
     booktitle = {},
     series = {Journ\'ees \'equations aux d\'eriv\'ees partielles},
     eid = {11},
     pages = {1--10},
     publisher = {Ecole polytechnique},
     year = {1987},
     mrnumber = {89a:58108},
     zbl = {0639.35065},
     language = {en},
     url = {http://archive.numdam.org/item/JEDP_1987____A11_0/}
}