@article{IM2_2001_65_4_a7,
     author = {K. B. Sabitov and A. A. Karamova},
     title = {Spectral properties of solutions of the {Tricomi} problem for equations of mixed type with two lines of degeneracy, and their applications},
     journal = {Izvestiya. Mathematics},
     pages = {769--785},
     year = {2001},
     volume = {65},
     number = {4},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/IM2_2001_65_4_a7/}
}