@book{MSM_1931__48__1_0,
     author = {Petrovitch, Michel},
     title = {Int\'egration qualitative des \'equations diff\'erentielles},
     series = {M\'emorial des sciences math\'ematiques},
     publisher = {Gauthier-Villars},
     number = {48},
     year = {1931},
     zbl = {0001.06002},
     language = {fr},
     url = {http://archive.numdam.org/item/MSM_1931__48__1_0/}
}