As mentioned above, in these geometric variables, as in any other canonical formulation of general relativity, one is faced with constraints, which encode the fact that the canonical variables cannot be specified independently. A familiar example of a constraint is Gauss’s law from ordinary electromagnetism, which states that, in the absence of charges, ∇·E(x) − 4πρ = 0 at every point x. It means that the three components of the electric field at every point must be chosen so as to satisfy this