@article{FPM_2006_12_7_a4,
     author = {A. V. Zhiber and R. D. Murtazina},
     title = {On the characteristic {Lie} algebras for equations $u_{xy}=f(u,u_x)$},
     journal = {Fundamentalʹna\^a i prikladna\^a matematika},
     pages = {65--78},
     publisher = {mathdoc},
     volume = {12},
     number = {7},
     year = {2006},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/FPM_2006_12_7_a4/}
}