@article{RLIN_1996_9_7_4_a5,
     author = {Valent, Tullio},
     title = {A perturbation problem in the presence of affine symmetries},
     journal = {Atti della Accademia nazionale dei Lincei. Rendiconti Lincei. Matematica e applicazioni},
     pages = {253--266},
     publisher = {mathdoc},
     volume = {Ser. 9, 7},
     number = {4},
     year = {1996},
     zbl = {0881.47009},
     mrnumber = {448362},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/RLIN_1996_9_7_4_a5/}
}