@article{VMUMM_1987_4_a9,
     author = {G. V. Osinnikova and I. N. Sergeev},
     title = {The unattainability of central indices in a class of regular systems},
     journal = {Vestnik Moskovskogo universiteta. Matematika, mehanika},
     pages = {39--44},
     publisher = {mathdoc},
     number = {4},
     year = {1987},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/VMUMM_1987_4_a9/}
}