@article{DAN_1976_228_6_a1,
     author = {S. M. Vishik},
     title = {On invariant characteristics of quadratically nonlinear systems of cascade type},
     journal = {Doklady Akademii Nauk},
     pages = {1269--1272},
     publisher = {mathdoc},
     volume = {228},
     number = {6},
     year = {1976},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DAN_1976_228_6_a1/}
}