@article{JRAM_1995__473_153808,
     author = {Bj\"orn Gustafsson and Henrik Shahgholian},
     title = {Existence and geometric properties of solutions of a free boundary problem in potential theory.},
     journal = {Journal f\"ur die reine und angewandte Mathematik},
     pages = {137--180},
     publisher = {mathdoc},
     volume = {473},
     year = {1995},
     zbl = {0846.31005},
     url = {http://geodesic.mathdoc.fr/item/JRAM_1995__473_153808/}
}