[7] D. Krupka: A geometric theory of ordinary first order variational problems in fibered manifolds, I. Critical sections, J. Math. Anal. Appl. 49 (1975), 180-206. MR 0362397 | Zbl 0312.58002

[8] D. Krupka: On the local structure of the Euler-Lagrange mapping of the calculus of variations. Proc. Conf. on Diff. Geom. and Appl., Nové Město na Moravě, Sept. 1980; Univerzita Karlova, Prague (Czechoslovakia), 1982, 181-188. MR 0663224

[9] D. Krupka: Some geometric aspects of variational problems in fibered manifolds. Folia Fac. Sci. Nat. UJEP Brunensis, 14, 1973.

[10] B. Kupershmidt: Geometry of jet bundles and the structure of Lagrangian and Hamiltonian formalisms. Lecture Notes in Math. 775, Springer, Berlin, 1980, 162-218. MR 0569303 | Zbl 0439.58016

[11] F. Takens: A global version of the inverse problem of the calculus of variations. J. Differential Geom. 14 (1979), 543-562. MR 0600611 | Zbl 0463.58015

[12] W. Tulczyjew: The Euler-Lagrange resolution. Internat. Colloquium on Diff. Geom. Methods in Math. Physics, Aix-en-Provence, Sept. 1979; Lecture Notes in Math. 836, Springer, Berlin, 1980, 22-48. MR 0607685