A geometrical analysis of the field equations in field theory. Echeverría-Enríquez, A.; Muñoz-Lecanda, M.C.; Román-Roy, N. — 2002 International Journal of Mathematics and Mathematical Sciences
Variational calculus in several variables : a hamiltonian approach A. Echeverría Enríquez; M. C. Muñoz Lecanda — 1992 Annales de l'I.H.P. Physique théorique