@article{ZNSL_1990_180_a2,
     author = {R. F. Bikbaev},
     title = {Hiperbolic {Whitham} systems and integrable equations},
     journal = {Zapiski Nauchnykh Seminarov POMI},
     pages = {23--35},
     year = {1990},
     volume = {180},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/ZNSL_1990_180_a2/}
}