@article{AIF_1976__26_4_239_0,
     author = {Varela, Fernando},
     title = {Formes de {Pfaff,} classe et perturbations},
     journal = {Annales de l'Institut Fourier},
     pages = {239--271},
     publisher = {Imprimerie Durand},
     address = {Chartres},
     volume = {26},
     number = {4},
     year = {1976},
     doi = {10.5802/aif.639},
     mrnumber = {57 #17679},
     zbl = {0331.58003},
     language = {fr},
     url = {http://archive.numdam.org/articles/10.5802/aif.639/}
}