@book{MSM_1929__37__1_0,
     author = {Cerf, G.},
     title = {Transformations de contact et probl\`eme de {Pfaff}},
     series = {M\'emorial des sciences math\'ematiques},
     year = {1929},
     publisher = {Gauthier-Villars},
     number = {37},
     language = {fr},
     url = {https://www.numdam.org/item/MSM_1929__37__1_0/}
}