@article{TSP_2006_25_25_a10,
     author = {I. N. Sergeev},
     title = {Definition and properties of characteristic frequencies of a linear equation},
     journal = {Trudy Seminara im. I.G. Petrovskogo},
     pages = {249--294},
     year = {2006},
     volume = {25},
     number = {25},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/TSP_2006_25_25_a10/}
}