%0 Journal Article %A S. J. Bilchev %T Systems of two first order partial differential equations (the conservation laws) %J Izvestiâ vysših učebnyh zavedenij. Matematika %D 1970 %P 28-34 %N 6 %I mathdoc %U http://geodesic.mathdoc.fr/item/IVM_1970_6_a3/ %G ru %F IVM_1970_6_a3