@article{ZNSL_2003_300_a11,
     author = {H. R. Dullin and A. V. Ivanov},
     title = {Twistless tori near low order resonances},
     journal = {Zapiski Nauchnykh Seminarov POMI},
     pages = {135--144},
     publisher = {mathdoc},
     volume = {300},
     year = {2003},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/ZNSL_2003_300_a11/}
}