@article{MZ_1959__71_169808,
     author = {Philip Hartman},
     title = {On solutions of {...V+V} = 0 in an exterior region.},
     journal = {Mathematische Zeitschrift},
     pages = {251--257},
     publisher = {mathdoc},
     volume = {71},
     year = {1959},
     zbl = {0092.31402},
     url = {http://geodesic.mathdoc.fr/item/MZ_1959__71_169808/}
}