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

[1] D.C. Clark, A variant of the Lusternick-Schnirelman Theory, Indiana J. Math 22, (1972) 65-74. | MR 296777 | Zbl 0228.58006

[2] G. Fournier, A Simplicial Approach to the Fixed Point Index, Fixed Point Theory, Sherbrooke, Quebec 1980, Edited by E. Fadell and G. Fournier, Springer-Verlag 886. 73-102 | MR 643000 | Zbl 0482.55003

[3] G. Fournier -J. Mawhin, On Periodic Solutions of Forced Pendulum-like Equations, J.Differential Equations 60(1985), 381-395. | MR 811773 | Zbl 0616.34014

[4] J. Mawhin -M. Willem, Multiple solutions of the periodic boundary value problem for some forced pendulum-type equations, J.Differential Equations 52(1984), 264-287. | MR 741271 | Zbl 0557.34036

[5] W.M. Ni, Some Minimax Principles and their Applications in nonlinear Elliptic Equations, Journal d'analyse mathématiques 37( 1980), 248-275. | MR 583639 | Zbl 0462.58016

[6] R. Palais, The Lusternik-Schnirelman theory on Banach manifolds, Topology 5(1966), 115-132. | MR 259955 | Zbl 0143.35203

[7] A. Capozzi ,D. Fortunato and A. Salvatore, Periodic Solutions of Lagrahgian Systems with Bounded Potential, Preprint. | MR 887004