@article{TIMM_2007_13_4_a6,
     author = {A. V. Zhiber and Yu. G. Mikhailova},
     title = {On hyperbolic systems of equations with zero generalized {Laplace} invariants},
     journal = {Trudy Instituta matematiki i mehaniki},
     pages = {74--83},
     publisher = {mathdoc},
     volume = {13},
     number = {4},
     year = {2007},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/TIMM_2007_13_4_a6/}
}