On the Hölder continuity of solutions of second order elliptic equations in two variables
Annali della Scuola Normale Superiore di Pisa - Classe di Scienze, Serie 3, Volume 26 (1972) no. 2, p. 391-402 
@article{ASNSP_1972_3_26_2_391_0,
     author = {Piccinini, Livio C. and Spagnolo, Sergio},
     title = {On the H\"older continuity of solutions of second order elliptic equations in two variables},
     journal = {Annali della Scuola Normale Superiore di Pisa - Classe di Scienze},
     publisher = {Scuola normale superiore},
     volume = {Ser. 3, 26},
     number = {2},
     year = {1972},
     pages = {391-402},
     zbl = {0237.35028},
     mrnumber = {361422},
     language = {en},
     url = {http://www.numdam.org/item/ASNSP_1972_3_26_2_391_0}
}

Piccinini, L. C.; Spagnolo, S. On the Hölder continuity of solutions of second order elliptic equations in two variables. Annali della Scuola Normale Superiore di Pisa - Classe di Scienze, Serie 3, Volume 26 (1972) no. 2, pp. 391-402. http://www.numdam.org/item/ASNSP_1972_3_26_2_391_0/

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