@article{AIHPC_1996__13_1_17_0,
     author = {Horozov, Emil Ivanov and Iliev, Iliya Dimov},
     title = {Perturbations of quadratic hamiltonian systems with symmetry},
     journal = {Annales de l'I.H.P. Analyse non lin\'eaire},
     pages = {17--56},
     publisher = {Gauthier-Villars},
     volume = {13},
     number = {1},
     year = {1996},
     mrnumber = {1373471},
     zbl = {0854.34035},
     language = {en},
     url = {http://archive.numdam.org/item/AIHPC_1996__13_1_17_0/}
}