@article{DE_1994_30_3_a11,
     author = {M. B. Sheftel},
     title = {Group analysis of defining equations~{\textendash} a method for finding recursion operators},
     journal = {Differencialʹnye uravneni\^a},
     pages = {444--456},
     year = {1994},
     volume = {30},
     number = {3},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DE_1994_30_3_a11/}
}