@article{MO_2021_100_4_a8,
     author = {V. V. Ivlev and E. A. Krivoshey},
     title = {Approximation of the {Pfaff} equations of several variables},
     journal = {Matemati\v{c}eskoe obrazovanie},
     pages = {57--62},
     publisher = {mathdoc},
     volume = {100},
     number = {4},
     year = {2021},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/MO_2021_100_4_a8/}
}