@article{DAN_1958_122_6_a4,
     author = {I. S. Kats},
     title = {Some general theorems on the behaviour of spectral functions of second order differential systems},
     journal = {Doklady Akademii Nauk},
     pages = {974--977},
     publisher = {mathdoc},
     volume = {122},
     number = {6},
     year = {1958},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DAN_1958_122_6_a4/}
}