@article{IVM_1974_1_a0,
     author = {S. J. Bilchev},
     title = {The linearity of systems of two first order partial differential equations},
     journal = {Izvesti\^a vys\v{s}ih u\v{c}ebnyh zavedenij. Matematika},
     pages = {3--14},
     publisher = {mathdoc},
     number = {1},
     year = {1974},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/IVM_1974_1_a0/}
}