1. R.J. Alonso-Blanco, J. Muñoz-Dı́az, The contact system for A-jet manifolds, Arch. Math. (Brno), in press
2. Mathematical Methods of Classical Mechanics;Arnol'd,1992
3. Sur les systèmes complètement orthogonaux dans l'espace à n dimensions et sur la réduction des systèmes différentielles les plus généraux;Drach;C. R. Acad. Sci.,1897
4. On the reduction of some systems of partial differential equations to first order systems with only one unknown function;Jiménez,2002
5. S. Jiménez, J. Muñoz, J. Rodrı́guez, Correspondences between jet spaces and PDE systems, submitted for publication