@article{DAN_1969_185_3_a3,
     author = {Yu. V. Egorov},
     title = {A priori estimates for first order differential operators},
     journal = {Doklady Akademii Nauk},
     pages = {507--508},
     publisher = {mathdoc},
     volume = {185},
     number = {3},
     year = {1969},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DAN_1969_185_3_a3/}
}