@article{JSFU_2010_3_2_a4,
     author = {Anatoly V. Zhiber and Olga S. Kostrigina},
     title = {Characteristic algebras of nonlinear hyperbolic systems of equations},
     journal = {\v{Z}urnal Sibirskogo federalʹnogo universiteta. Matematika i fizika},
     pages = {173--184},
     year = {2010},
     volume = {3},
     number = {2},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/JSFU_2010_3_2_a4/}
}