DUAL-NULL DYNAMICS

Generalised Lagrangian and Hamiltonian theories of dynamics with two e volution directions are presented. The corresponding evolution problem involves prescribing initial data on two intersecting surfaces. In th e dual-null case, where the initial surfaces are null (or characterist ic), and a certain functional is invertible, the initial data are the appropriate momentum field on each surface, and the configuration fiel d on the intersection. The theory is applied to the Klein-Gordon and M axwell fields, and the relativistic string.