@incollection{JEDP_1987____A2_0,
     author = {Lerner, Nicolas},
     title = {Sufficiency of condition ($\psi $) for local solvability in two dimensions},
     booktitle = {},
     series = {Journ\'ees \'equations aux d\'eriv\'ees partielles},
     eid = {2},
     pages = {1--23},
     publisher = {Ecole polytechnique},
     year = {1987},
     mrnumber = {89e:35150},
     zbl = {0636.58032},
     language = {en},
     url = {http://archive.numdam.org/item/JEDP_1987____A2_0/}
}