@article{MZ_1961__75_169917,
     author = {Philip Hartman and Calvin Wilcox},
     title = {On solutions of the {Helmholtz} equation in exterior domains.},
     journal = {Mathematische Zeitschrift},
     pages = {228--255},
     publisher = {mathdoc},
     volume = {75},
     year = {1961},
     zbl = {0096.07601},
     url = {http://geodesic.mathdoc.fr/item/MZ_1961__75_169917/}
}