@article{DE_1985_21_3_a28,
     author = {V. M. Filippov},
     title = {A general approach to symmetrization of differential operators},
     journal = {Differencialʹnye uravneni\^a},
     pages = {539--541},
     publisher = {mathdoc},
     volume = {21},
     number = {3},
     year = {1985},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DE_1985_21_3_a28/}
}