@article{DAN_1967_175_1_a9,
     author = {G. A. Utkin},
     title = {Topological classification of non-singular fourth-order surfaces},
     journal = {Doklady Akademii Nauk},
     pages = {40--43},
     publisher = {mathdoc},
     volume = {175},
     number = {1},
     year = {1967},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DAN_1967_175_1_a9/}
}