@article{DE_1985_21_2_a10,
     author = {D. Kh. Safarov},
     title = {Systems of first-order partial differential equations of composite type},
     journal = {Differencialʹnye uravneni\^a},
     pages = {272--276},
     publisher = {mathdoc},
     volume = {21},
     number = {2},
     year = {1985},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DE_1985_21_2_a10/}
}