@article{ZVMMF_1998_38_1_a7,
     author = {A. A. Abramov and V. I. Ul'yanova and L. F. Yukhno},
     title = {The argument principle in a spectral problem for systems of ordinary differential equations with singularities},
     journal = {\v{Z}urnal vy\v{c}islitelʹnoj matematiki i matemati\v{c}eskoj fiziki},
     pages = {61--67},
     publisher = {mathdoc},
     volume = {38},
     number = {1},
     year = {1998},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/ZVMMF_1998_38_1_a7/}
}