%0 Journal Article %T Null Surfaces and Legendre Submanifolds %A Mirta Iriondo %A Carlos Kozameh %A Alejandra Rojas %J Physics %D 1998 %I arXiv %R 10.1063/1.533077 %X It is shown that the main variable Z of the Null Surface Formulation of GR is the generating function of a constrained Lagrange submanifold that lives on the energy surface H=0 and that its level surfaces Z=const. are Legendre submanifolds on that energy surface. The behaviour of the variable Z at the caustic points is analysed and a genralization of this variable is discussed. %U http://arxiv.org/abs/gr-qc/9805027v1