@article{RM_2001_56_3_a1,
     author = {V. G. Gelfreich and V. F. Lazutkin},
     title = {Splitting of separatrices: perturbation theory and exponential smallness},
     journal = {Trudy Matematicheskogo Instituta imeni V.A. Steklova},
     pages = {499--558},
     publisher = {mathdoc},
     volume = {56},
     number = {3},
     year = {2001},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/RM_2001_56_3_a1/}
}