@article{ZNSL_1999_259_a1,
     author = {M. I. Belishev and S. A. Ivanov},
     title = {Characterization of data in the dynamical inverse problem for two-velocity system},
     journal = {Zapiski Nauchnykh Seminarov POMI},
     pages = {19--45},
     publisher = {mathdoc},
     volume = {259},
     year = {1999},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/ZNSL_1999_259_a1/}
}