@article{JEDP_1988____A1_0,
     author = {Beals, Richard},
     title = {Calcul pseudodiff\'erentiel trois-\'etape},
     journal = {Journ\'ees \'equations aux d\'eriv\'ees partielles},
     eid = {1},
     pages = {1--4},
     publisher = {Ecole polytechnique},
     year = {1988},
     mrnumber = {975490},
     zbl = {0661.35020},
     language = {fr},
     url = {http://archive.numdam.org/item/JEDP_1988____A1_0/}
}