In this limit the Einstein equation reduces to a linear wave equation.

So it appears constants in the Einstein equation cannot vary, otherwise this postulate would be violated.

The variation with respect to the metric tensor yields the Einstein equations:

We will derive the Einstein equations by varying this action with respect to the tetrad and spin connection as independent quantities.

From its solutions to the Einstein equations, he predicts the distance-redshift relation.

Three he suspected were old friends: the Einstein equations, with modifications for quantum effects when the length scale became small enough.

The vanishing of the constraints, giving the physical phase space, are the four other Einstein equations.

His masters thesis was entitled: Generation of solutions to the Einstein equations.

The above are solutions to Einstein equations in vacuum.

David, the Einstein equation itself is a field equation for the metric.