“…The formulation is in terms of two functions, Ω(x, S 2 ) and Z(x, S 2 ), of the space-time points, x a , and parametrized by points on the sphere, i.e., by functions on the sphere-bundle over a space-time manifold, functions on R 4 xS 2 . The first of the functions Ω, is to be considered as a conformal factor for a sphere's worth of conformal metrics -the factor turning the conformal metrics into Einstein metrics -while the second function, Z, describes, at each space-time point, a sphere's worth of characteristic surfaces.…”