%0 Journal Article %A V. V. Ivlev %A E. A. Krivoshey %T Approximation of the Pfaff equations of several variables %J Matematičeskoe obrazovanie %D 2021 %P 57-62 %N 4 %U http://geodesic.mathdoc.fr/item/MO_2021_4_a8/ %G ru %F MO_2021_4_a8