@article{JEDP_1989____A5_0,
     author = {Liess, Otto},
     title = {Global existence for the nonlinear equations of crystal optics},
     journal = {Journ\'ees \'equations aux d\'eriv\'ees partielles},
     eid = {5},
     pages = {1--11},
     publisher = {Ecole polytechnique},
     year = {1989},
     zbl = {0688.35091},
     mrnumber = {1030820},
     language = {en},
     url = {http://www.numdam.org/item/JEDP_1989____A5_0/}
}