1. FerrarisM. and FrancavigliaM., in M.Modugno (ed), Proc. International Meeting on Geometry and Physics, Florence, October 12?15, 1982, Pitagora Editrice, Bologna, 1983, p. 43.
2. CrampinM., SarletW., and CantrijnF., Math. Proc. Cam. Phil. Soc. 99, 565 (1986).
3. London Mathematical Society Lecture Note Series;D. J. Saunders,1989
4. Gràcia, X., Pons, J. M., and Román-Roy, N., Higher-order Lagrangian systems: some geometric structures, preprint UB-ECM-PF 1/89, Universitat de Barcelona.
5. de León, M. and Lacomba, E. A., Lagrangian submanifolds and higher-order mechanical systems, preprint CECIME, Madrid.