A convex Darboux theorem
Annali della Scuola Normale Superiore di Pisa - Classe di Scienze, Serie 4, Volume 25 (1997) no. 1-2, p. 287-297 
@article{ASNSP_1997_4_25_1-2_287_0,
     author = {Chiappori, Pierre-Andr\'e and Ekeland, Ivar},
     title = {A convex Darboux theorem},
     journal = {Annali della Scuola Normale Superiore di Pisa - Classe di Scienze},
     publisher = {Scuola normale superiore},
     volume = {Ser. 4, 25},
     number = {1-2},
     year = {1997},
     pages = {287-297},
     zbl = {1004.58501},
     mrnumber = {1655519},
     language = {en},
     url = {http://www.numdam.org/item/ASNSP_1997_4_25_1-2_287_0}
}

Chiappori, Pierre-André; Ekeland, Ivar. A convex Darboux theorem. Annali della Scuola Normale Superiore di Pisa - Classe di Scienze, Serie 4, Volume 25 (1997) no. 1-2, pp. 287-297. http://www.numdam.org/item/ASNSP_1997_4_25_1-2_287_0/

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