@article{SM_1995_82_1_a11,
     author = {L. D. Pustyl'nikov},
     title = {Existence of invariant curves for maps close to degenerate maps, and a~solution of {the~Fermi--Ulam} problem},
     journal = {Sbornik. Mathematics},
     pages = {231--241},
     publisher = {mathdoc},
     volume = {82},
     number = {1},
     year = {1995},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/SM_1995_82_1_a11/}
}