@article{10_1090_S0894_0347_03_00422_3,
     author = {Chen, Gui-Qiang and Feldman, Mikhail},
     title = {Multidimensional transonic shocks and free boundary problems for nonlinear equations of mixed type},
     journal = {Journal of the American Mathematical Society},
     pages = {461--494},
     publisher = {mathdoc},
     volume = {16},
     number = {3},
     year = {2003},
     doi = {10.1090/S0894-0347-03-00422-3},
     url = {http://geodesic.mathdoc.fr/articles/10.1090/S0894-0347-03-00422-3/}
}