A comparison theorem for nonlinear operators
Annali della Scuola Normale Superiore di Pisa - Scienze Fisiche e Matematiche, Série 3, Tome 25 (1971) no. 1, pp. 41-46. 
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     author = {Allegretto, W.},
     title = {A comparison theorem for nonlinear operators},
     journal = {Annali della Scuola Normale Superiore di Pisa - Scienze Fisiche e Matematiche},
     pages = {41--46},
     publisher = {Scuola normale superiore},
     volume = {Ser. 3, 25},
     number = {1},
     year = {1971},
     mrnumber = {298181},
     zbl = {0225.35013},
     language = {en},
     url = {http://archive.numdam.org/item/ASNSP_1971_3_25_1_41_0/}
}
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Allegretto, W. A comparison theorem for nonlinear operators. Annali della Scuola Normale Superiore di Pisa - Scienze Fisiche e Matematiche, Série 3, Tome 25 (1971) no. 1, pp. 41-46. http://archive.numdam.org/item/ASNSP_1971_3_25_1_41_0/

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