Smoothness and analyticity of free boundaries in variational inequalities
Annali della Scuola Normale Superiore di Pisa - Classe di Scienze, Serie 4, Volume 3 (1976) no. 2, p. 289-310 
@article{ASNSP_1976_4_3_2_289_0,
     author = {Caffarelli, Luis and Rivi\`ere, N. M.},
     title = {Smoothness and analyticity of free boundaries in variational inequalities},
     journal = {Annali della Scuola Normale Superiore di Pisa - Classe di Scienze},
     publisher = {Scuola normale superiore},
     volume = {Ser. 4, 3},
     number = {2},
     year = {1976},
     pages = {289-310},
     zbl = {0363.35009},
     mrnumber = {412940},
     language = {en},
     url = {http://www.numdam.org/item/ASNSP_1976_4_3_2_289_0}
}

Caffarelli, L. A.; Rivière, N. M. Smoothness and analyticity of free boundaries in variational inequalities. Annali della Scuola Normale Superiore di Pisa - Classe di Scienze, Serie 4, Volume 3 (1976) no. 2, pp. 289-310. http://www.numdam.org/item/ASNSP_1976_4_3_2_289_0/

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