1. Aldaya, V., and de Azcárraga, J.A., “Variational principles on rth order jets of fibre bundles in field theory”, Journal of Mathematical Physics, 19 (1978), pp. 1869–1875.
2. Binz, E., Śniatycki, J., and Fischer, H., Geometry of Classical Fields, Elsevier Science Publishers, New York, 1988. Reprinted by Dover Publications, Mineola N.Y., 2006.
3. Campos, C.M., Geometric Methods in Classical Field Theory and Continuous Media, Thesis, Departamento de Mathemáticas, Facultad de Ciencias, Universidad Autónoma de Madrid, 2010.
4. Cartan, É., “Les espaces métriques fondés sur la notion d’aire”, Actualités Scientifique et Industrielles, no 72 (1933). Reprinted by Hermann, Paris, 1971.
5. De Donder, Th., “Théorie invariantive du calcul des variations”, Bull, Acad. de Belg. 1929, chap. 1. [this reference appears in Cartan [4]].