no. 4
Regularity in elliptic free boundary problems. II. Equations of higher order
Annali della Scuola Normale Superiore di Pisa - Classe di Scienze, Série 4, Tome 6 (1979) no. 4, pp. 637-683. 
@article{ASNSP_1979_4_6_4_637_0,
     author = {Kinderlehrer, David and Nirenberg, Louis and Spruck, Joel},
     title = {Regularity in elliptic free boundary problems. II. Equations of higher order},
     journal = {Annali della Scuola Normale Superiore di Pisa - Classe di Scienze},
     pages = {637--683},
     publisher = {Scuola normale superiore},
     volume = {Ser. 4, 6},
     number = {4},
     year = {1979},
     zbl = {0425.35097},
     mrnumber = {563338},
     language = {en},
     url = {www.numdam.org/item/ASNSP_1979_4_6_4_637_0/}
}
Kinderlehrer, D.; Nirenberg, L.; Spruck, J. Regularity in elliptic free boundary problems. II. Equations of higher order. Annali della Scuola Normale Superiore di Pisa - Classe di Scienze, Série 4, Tome 6 (1979) no. 4, pp. 637-683. http://www.numdam.org/item/ASNSP_1979_4_6_4_637_0/

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