1. Variational principles for locally variational forms;Brajerčík;J. Math. Phys.,2005
2. New Lagrangian and Hamiltonian Methods in Field Theory;Giachetta,1997
3. Natural Operations in Differential Geometry;Kolář,1993
4. Some geometric aspects of variational problems in fibred manifolds;Krupka;Folia Fac. Sci. Nat. Univ. Purk. Brunensis, Physica,1973