@article{DAN_1969_185_3_a2,
     author = {V. V. Velichenko},
     title = {The invariance of discrete systems},
     journal = {Doklady Akademii Nauk},
     pages = {503--506},
     publisher = {mathdoc},
     volume = {185},
     number = {3},
     year = {1969},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DAN_1969_185_3_a2/}
}