@article{MO_2018_4_a4,
     author = {V. V. Ivlev and E. M. Arkhipova},
     title = {On an approximation of {Pfaff's} equations},
     journal = {Matemati\v{c}eskoe obrazovanie},
     pages = {30--37},
     year = {2018},
     number = {4},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/MO_2018_4_a4/}
}