A regularity theorem for linear second order elliptic divergence equations
Annali della Scuola Normale Superiore di Pisa - Classe di Scienze, Serie 3, Volume 26 (1972) no. 2, p. 283-290 
@article{ASNSP_1972_3_26_2_283_0,
     author = {Hager, R. A. and Ross, J.},
     title = {A regularity theorem for linear second order elliptic divergence equations},
     journal = {Annali della Scuola Normale Superiore di Pisa - Classe di Scienze},
     publisher = {Scuola normale superiore},
     volume = {Ser. 3, 26},
     number = {2},
     year = {1972},
     pages = {283-290},
     zbl = {0256.35027},
     mrnumber = {374643},
     language = {en},
     url = {http://www.numdam.org/item/ASNSP_1972_3_26_2_283_0}
}

Hager, R. A.; Ross, J. A regularity theorem for linear second order elliptic divergence equations. Annali della Scuola Normale Superiore di Pisa - Classe di Scienze, Serie 3, Volume 26 (1972) no. 2, pp. 283-290. http://www.numdam.org/item/ASNSP_1972_3_26_2_283_0/

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