Consistent Hamiltonian Reduction

This is the authors' abstract. We don't add key points for this paper.

I show that the recently proposed (2+2) Hamiltonian reduction of Einstein's equations of 4-dimensional spacetimes is consistent with general covariance. The consistency proof is { extrinsic}, as it follows from the fact that Hamilton's equations derived from the non-zero gravitational Hamiltonian are identical to the Ricci-flat condition of 4-dimensional spacetimes in privileged coordinates.