@article{AUPO_1987__26_1_a7,
     author = {Andres, J\'an},
     title = {Symmetry in a certain simply perturbed {Hamiltonian} system},
     journal = {Acta Universitatis Palackianae Olomucensis. Facultas Rerum Naturalium. Mathematica},
     pages = {131--138},
     publisher = {mathdoc},
     volume = {26},
     number = {1},
     year = {1987},
     mrnumber = {1033334},
     zbl = {0699.34046},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/AUPO_1987__26_1_a7/}
}