An inversion of the obstacle problem and its explicit solution
Annali della Scuola Normale Superiore di Pisa - Classe di Scienze, Serie 4, Volume 6 (1979) no. 4, p. 561-571 
@article{ASNSP_1979_4_6_4_561_0,
     author = {Lewy, Hans},
     title = {An inversion of the obstacle problem and its explicit solution},
     journal = {Annali della Scuola Normale Superiore di Pisa - Classe di Scienze},
     publisher = {Scuola normale superiore},
     volume = {Ser. 4, 6},
     number = {4},
     year = {1979},
     pages = {561-571},
     zbl = {0428.35080},
     mrnumber = {563334},
     language = {en},
     url = {http://www.numdam.org/item/ASNSP_1979_4_6_4_561_0}
}

Lewy, Hans. An inversion of the obstacle problem and its explicit solution. Annali della Scuola Normale Superiore di Pisa - Classe di Scienze, Serie 4, Volume 6 (1979) no. 4, pp. 561-571. http://www.numdam.org/item/ASNSP_1979_4_6_4_561_0/

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