@article{DAN_1980_251_5_a10,
     author = {S. M. Ponomarev},
     title = {On an eigenvalue problem for an equation of mixed type},
     journal = {Doklady Akademii Nauk},
     pages = {1070--1072},
     publisher = {mathdoc},
     volume = {251},
     number = {5},
     year = {1980},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DAN_1980_251_5_a10/}
}