@incollection{JEDP_1993____A1_0,
     author = {Fabrice B\'ethuel and Jean-Michel Ghidaglia},
     title = {R\'egularit\'e des solutions de certaines \'equations elliptiques en dimension deux et formule de la co-aire},
     booktitle = {},
     series = {Journ\'ees \'equations aux d\'eriv\'ees partielles},
     eid = {1},
     pages = {1--36},
     publisher = {\'Ecole polytechnique},
     year = {1993},
     doi = {10.5802/jedp.440},
     mrnumber = {94k:35044},
     zbl = {0812.35037},
     language = {fr},
     url = {https://proceedings.centre-mersenne.org/articles/10.5802/jedp.440/}
}