@article{MAT_1961_5_2_a8,
     author = {C. L. Siegel},
     title = {On the integrals of canonical systems},
     journal = {Matematika},
     pages = {103--118},
     year = {1961},
     volume = {5},
     number = {2},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/MAT_1961_5_2_a8/}
}