@article{AM_2000_151_1_a7,
     author = {Luis A. Caffarelli and Lavi Karp and Henrik Shahgholian},
     title = {Regularity of a free boundary with application to the {Pompeiu} problem},
     journal = {Annals of mathematics},
     publisher = {mathdoc},
     volume = {151},
     number = {1},
     year = {2000},
     url = {http://geodesic.mathdoc.fr/item/AM_2000_151_1_a7/}
}