 From this, (3) quantum mechanics can be seen to emerge via the correspondence principle, as a nonrelativistic approximation for a theory of inertia in relativity.The result is a continuous quaternion-based formalism modeling all manifestations of matter.Sachs called the transformation symmetry group that Einstein sought in completing general covariance 'the Einstein group', which approaches the Poincaré group towards the flat spacetime of special relativity.