@article{FAA_1991_25_4_a2,
     author = {A. T. Fomenko},
     title = {A topological invariant which roughly classifies integrable strictly nondegenerate {Hamiltonians} on four-dimensional symplectic manifolds},
     journal = {Funkcionalʹnyj analiz i ego prilo\v{z}eni\^a},
     pages = {23--35},
     publisher = {mathdoc},
     volume = {25},
     number = {4},
     year = {1991},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/FAA_1991_25_4_a2/}
}