@article{JEMS_2010_12_5_a3,
     author = {Luis A. Caffarelli and Jean-Michel Roquejoffre and Yannick Sire},
     title = {Variational problems with free boundaries for the fractional {Laplacian}},
     journal = {Journal of the European Mathematical Society},
     pages = {1151--1179},
     publisher = {mathdoc},
     volume = {12},
     number = {5},
     year = {2010},
     doi = {10.4171/jems/226},
     url = {http://geodesic.mathdoc.fr/articles/10.4171/jems/226/}
}