@article{MZM_1992_52_5_a8,
     author = {A. G. Kushner},
     title = {Chaplygin and {Keldysh} normal forms of {Monge--Ampere} equations of variable type},
     journal = {Matemati\v{c}eskie zametki},
     pages = {63--67},
     publisher = {mathdoc},
     volume = {52},
     number = {5},
     year = {1992},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/MZM_1992_52_5_a8/}
}