@article{IM2_1991_36_2_a8,
     author = {A. M. Samoilenko and R. I. Petrishin},
     title = {On integral manifolds of multifrequency oscillatory systems},
     journal = {Izvestiya. Mathematics },
     pages = {391--409},
     publisher = {mathdoc},
     volume = {36},
     number = {2},
     year = {1991},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/IM2_1991_36_2_a8/}
}