An imbedding theorem in the calculus of variations for multiple integrals,addendum

It is shown how a set of canonical variables in the sense of Rund [5] can be associated with a given extremal of a multiple integral variational problem in a simple, direct manner. The definition of these variables in a previous paper [1], which is concerned with the problem of imbedding a given extremal in anr-geodesic field, is thereby clarified and abbreviated considerably. A theorem due essentially to Boerner, which is crucial to the imbedding theorem given in [1], is proved more easily and under less restrictive hypotheses than in [1]. Furthermore, it is shown how the present definition of the canonical variables allows one to eliminate from the geodesic field theory of Carathéodory the restriction that the Lagrangian be non-vanishing along the extremal.