@article{DE_1972_8_5_a13,
     author = {V. I. Plotnikov and V. I. Sumin},
     title = {Problems of the stability of nonlinear {Goursat{\textendash}Darboux} systems},
     journal = {Differencialʹnye uravneni\^a},
     pages = {845--856},
     year = {1972},
     volume = {8},
     number = {5},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DE_1972_8_5_a13/}
}