@article{SEDP_1981-1982____A23_0,
     author = {Berestycki, H.},
     title = {Orbites p\'eriodiques de syst\`emes conservatifs},
     journal = {S\'eminaire \'Equations aux d\'eriv\'ees partielles (Polytechnique) dit aussi "S\'eminaire Goulaouic-Schwartz"},
     note = {talk:24},
     pages = {1--17},
     publisher = {Ecole Polytechnique, Centre de Math\'ematiques},
     year = {1981-1982},
     mrnumber = {671621},
     zbl = {0513.70020},
     language = {fr},
     url = {http://www.numdam.org/item/SEDP_1981-1982____A23_0/}
}