@article{AIHPC_1989__S6__259_0,
     author = {Fournier, G. and Willem, M.},
     title = {Multiple solutions of the forced double pendulum equation},
     journal = {Annales de l'I.H.P. Analyse non lin\'eaire},
     pages = {259--281},
     publisher = {Gauthier-Villars},
     volume = {S6},
     year = {1989},
     mrnumber = {1204018},
     zbl = {0683.70022},
     language = {en},
     url = {http://www.numdam.org/item/AIHPC_1989__S6__259_0/}
}