@book{MSM_1960__142__1_0,
     author = {Parsons, D. H.},
     title = {The extension of {Darboux's} method},
     series = {M\'emorial des sciences math\'ematiques},
     year = {1960},
     publisher = {Gauthier-Villars},
     number = {142},
     mrnumber = {124604},
     zbl = {0119.07901},
     language = {en},
     url = {https://www.numdam.org/item/MSM_1960__142__1_0/}
}