@article{VSGU_2009_8_a1,
     author = {I. P. Egorova},
     title = {The problem with periodicity conditions for the equations of mixed type with characteristic degeneracy},
     journal = {Vestnik Samarskogo universiteta. Estestvennonau\v{c}na\^a seri\^a},
     pages = {15--27},
     publisher = {mathdoc},
     number = {8},
     year = {2009},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/VSGU_2009_8_a1/}
}