@article{SM_1995_80_1_a5,
     author = {V. V. Kozlov and N. V. Denisova},
     title = {Symmetries and the~topology of dynamical systems with two degrees of freedom},
     journal = {Sbornik. Mathematics},
     pages = {105--124},
     publisher = {mathdoc},
     volume = {80},
     number = {1},
     year = {1995},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/SM_1995_80_1_a5/}
}