@article{DE_1970_6_3_a20,
     author = {G. A. Los'},
     title = {Theorems on the estimation of the invariant $A_1$ of the characteristic equation for an $n$th order linear homogeneous 
},
     journal = {Differencialʹnye uravneni\^a},
     pages = {561--564},
     publisher = {mathdoc},
     volume = {6},
     number = {3},
     year = {1970},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DE_1970_6_3_a20/}
}