Other post-differential topological geometrical field structures are similarly restrictive. For example, the microsymmetry group of the conformal structure, which determines the causal structure of spacetime, permits 7 degrees of freedom (6 Lorentz transformations and a dilatation), and permits four more degrees of freedom in second order. Consequently, the existence of the conformal metrical field which determines at each point the cones of light propagation would prevent an arbitrary re