@article{10_1090_S0894_0347_08_00593_6,
     author = {Caffarelli, L. and Lin, Fang-Hua},
     title = {Singularly perturbed elliptic systems and multi-valued harmonic functions with free boundaries},
     journal = {Journal of the American Mathematical Society},
     pages = {847--862},
     publisher = {mathdoc},
     volume = {21},
     number = {3},
     year = {2008},
     doi = {10.1090/S0894-0347-08-00593-6},
     url = {http://geodesic.mathdoc.fr/articles/10.1090/S0894-0347-08-00593-6/}
}