no. 3
Monotonicity of the free boundary in the two-dimensional dam problem
Annali della Scuola Normale Superiore di Pisa - Classe di Scienze, Série 4, Tome 7 (1980) no. 3, pp. 523-537. 
@article{ASNSP_1980_4_7_3_523_0,
     author = {Caffarelli, Luis and Gilardi, Gianni},
     title = {Monotonicity of the free boundary in the two-dimensional dam problem},
     journal = {Annali della Scuola Normale Superiore di Pisa - Classe di Scienze},
     pages = {523--537},
     publisher = {Scuola normale superiore},
     volume = {Ser. 4, 7},
     number = {3},
     year = {1980},
     zbl = {0513.76090},
     mrnumber = {597551},
     language = {en},
     url = {archive.numdam.org/item/ASNSP_1980_4_7_3_523_0/}
}
Caffarelli, Luis A.; Gilardi, Gianni. Monotonicity of the free boundary in the two-dimensional dam problem. Annali della Scuola Normale Superiore di Pisa - Classe di Scienze, Série 4, Tome 7 (1980) no. 3, pp. 523-537. http://archive.numdam.org/item/ASNSP_1980_4_7_3_523_0/

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